Mascarenhas, John

Abstract Introduction: Thrombocytopenia, a hallmark of cytopenic myelofibrosis (MF), is associated with poor survival and quality of life impairment. Patients with MF and moderate or severe thrombocytopenia (platelet counts <100x10 9/L, <50x10 9/L) tend to have high symptom burden as measured by the Total Symptom Score (TSS), driven largely by physical functioning symptoms (Mesa R et al, ASH 2021 abstract in submission). Pacritinib, an investigational JAK2/IRAK1 inhibitor, was studied in patients with platelet counts ≤100x10 9/L in the PERSIST-2 trial. Unlike the pivotal studies upon which available JAK1/2 inhibitors were approved that relied on a modified TSS version that excluded 'tiredness' from the response analysis, PERSIST-2 included 'tiredness' as part of TSS and found response rates of 25% for pacritinib vs. 14% for best available therapy (BAT), P=0.08. Here, we retrospectively analyzed TSS on PERSIST-2 using the modified scoring system. In addition, we evaluated the impact of pacritinib and BAT, including ruxolitinib, on MF symptoms including 'tiredness' and 'inactivity'. Methods: All PERSIST-2 patients in the intention-to-treat population randomized at least 22 weeks prior to the end of the study were included. PERSIST-2 randomized patients 1:1:1 to pacritinib 200mg BID, pacritinib 400mg daily, or BAT (including ruxolitinib). The modified TSS score was calculated as the sum of individual symptom scores for early satiety, abdominal discomfort, rib pain, night sweats, itching, and bone pain ('tiredness' and 'inactivity' were not included), and response was defined as a ≥50% reduction in score from baseline to week 24. Symptoms were categorized as physical function-related (tiredness, inactivity), spleen-related (satiety, abdominal discomfort, rib pain), or cytokine-related (sweats, itching, bone pain). The Wilcoxon Rank Sum test was used to compare differences in scores. Results: The analysis included 74 patients randomized to pacritinib 200mg BID and 72 to BAT; an additional 75 were randomized to pacritinib 400mg QD (dose no longer in development). At baseline, 39% had moderate and 46% had severe thrombocytopenia. Ruxolitinib was selected as BAT in 45% of patients with moderate and 38% with severe thrombocytopenia. The co-primary endpoint for the study - TSS response rate in pooled pacritinib arms versus BAT - showed a significant difference using the modified TSS: 30% vs. 14%, P=0.008. Similarly, the modified TSS response rate was higher for patients treated with pacritinib 200mg BID compared to BAT (35% vs. 14%, P=0.004, Figure 1a). Among patients on the BAT arm, modified TSS response rates were modestly higher for patients who received ruxolitinib prior to week 24 (19% [n=6/32]) compared to those who did not (10% [n=4/40]), though both were lower than response rates with pacritinib. Patients on the pacritinib 200mg BID arm experienced greater percentage reductions in individual myelofibrosis symptoms between baseline and week 24 compared to BAT, both in patients with moderate and severe thrombocytopenia (Figure 1b, 1c). For physical function symptoms, severity was reduced more on pacritinib 200mg BID compared to BAT by week 24 (median reduction in tiredness: 30% vs. 13%, P=0.0261; inactivity: 22% vs. 7%, P=0.099). Among patients with severe thrombocytopenia, symptom improvement was minimal on BAT (Figure 1b). Conclusion: The symptom benefit of pacritinib in patients with moderate and severe thrombocytopenia is demonstrated in the PERSIST-2 study. A significant reduction in symptoms was observed in patients treated with pacritinib 200mg BID, the dose being studied in an ongoing Phase 3 trial (PACIFICA), compared to BAT. Furthermore, the modified TSS response rate of 35% in patients treated with pacritinib 200mg BID is comparable to that reported for approved JAK1/2 inhibitors in patients with higher platelet counts, suggesting the potential for pacritinib to address the unmet need of patients with cytopenic myelofibrosis. Figure 1 Figure 1. Disclosures Palmer: CTI BioPharma: Consultancy, Research Funding; Protagonist: Consultancy, Research Funding; Incyte: Research Funding; PharmaEssentia: Research Funding; Sierra Oncology: Consultancy, Research Funding. Mesa: Incyte Corporation: Consultancy, Research Funding; Samus: Research Funding; Sierra Oncology: Consultancy, Research Funding; CTI: Research Funding; Novartis: Consultancy; Celgene: Research Funding; Pharma: Consultancy; La Jolla Pharma: Consultancy; Constellation Pharmaceuticals: Consultancy, Research Funding; CTI: Research Funding; Abbvie: Research Funding; Gilead: Research Funding; Genentech: Research Funding; Promedior: Research Funding; AOP: Consultancy. Oh: Abbvie: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Membership on an entity's Board of Directors or advisory committees; Celgene Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees; Disc Medicine: Membership on an entity's Board of Directors or advisory committees; Geron: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Kartos Therapeutics: Membership on an entity's Board of Directors or advisory committees; PharamaEssentia: Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Membership on an entity's Board of Directors or advisory committees. Rampal: Sierra Oncology: Consultancy; Novartis: Consultancy; BMS/Celgene: Consultancy; Stemline: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy; Constellation: Research Funding; Kartos: Consultancy; Disc Medicine: Consultancy; Blueprint: Consultancy; Pharmaessentia: Consultancy; Incyte: Consultancy, Research Funding; Memorial Sloan Kettering: Current Employment; Abbvie: Consultancy; CTI: Consultancy. Buckley: CTI Biopharm: Current Employment. Roman-Torres: CTI Biopharm: Current Employment. Verstovsek: Protagonist Therapeutics: Research Funding; Genentech: Research Funding; Gilead: Research Funding; Incyte Corporation: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; NS Pharma: Research Funding; AstraZeneca: Research Funding; Blueprint Medicines Corp: Research Funding; CTI BioPharma: Research Funding; Promedior: Research Funding; Ital Pharma: Research Funding; PharmaEssentia: Research Funding; Roche: Research Funding; Novartis: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. Mascarenhas: Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merus: Research Funding; Geron: Consultancy; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Forbius: Research Funding; Genentech/Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy, Research Funding; Constellation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Promedior: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Prelude: Consultancy; Galecto: Consultancy; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Vannucchi: AbbVie: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees. Kiladjian: CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; AP Orphan: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Membership on an entity's Board of Directors or advisory committees. Harrison: Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Constellation Pharmaceuticals: Research Funding; Incyte Corporation: Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sierra Oncology: Honoraria; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Bose: Novartis: Honoraria; NS Pharma: Research Funding; Pfizer: Research Funding; Constellation Pharmaceuticals: Research Funding; Blueprint Medicines: Honoraria, Research Funding; Kartos Therapeutics: Honoraria, Research Funding; Incyte Corporation: Honoraria, Research Funding; Promedior: Research Funding; CTI BioPharma: Honoraria, Research Funding; Sierra Oncology: Honoraria; Astellas: Research Funding; BMS: Honoraria, Research Funding; Celgene Corporation: Honoraria, Research Funding. Craig: CTI BioPharma: Current Employment. Gerds: PharmaEssentia Corporation: Consultancy; CTI BioPharma: Research Funding; Sierra Oncology: Consultancy; AbbVie: Consultancy; Celgene/Bristol Myers Squibb: Consultancy; Constellation: Consultancy; Novartis: Consultancy.

Abstract Myelofibrosis (MF) is a clonal stem cell neoplasm characterized by abnormal JAK-STAT signaling, chronic inflammation, cytopenias, and risk of transformation to acute leukemia. Despite improvements in the therapeutic options for patients with MF, allogeneic hematopoietic stem cell transplantation remains the only curative treatment. We previously demonstrated multiple immunosuppressive mechanisms in patients with MF, including increased expression of programmed cell death protein 1 (PD-1) on T cells compared with healthy controls. Therefore, we conducted a multicenter, open-label, phase 2, single-arm study of pembrolizumab in patients with Dynamic International Prognostic Scoring System category of intermediate-2 or greater primary, post-essential thrombocythemia or post-polycythemia vera myelofibrosis that were ineligible for or were previously treated with ruxolitinib. The study followed a Simon 2-stage design and enrolled a total of 10 patients, 5 of whom had JAK2V617mutation, 2 had CALR mutation, and 6 had additional mutations. Most patients were previously treated with ruxolitinib. Pembrolizumab treatment was well tolerated, but there were no objective clinical responses, so the study closed after the first stage was completed. However, immune profiling by flow cytometry, T-cell receptor sequencing, and plasma proteomics demonstrated changes in the immune milieu of patients, which suggested improved T-cell responses that can potentially favor antitumor immunity. The fact that these changes were not reflected in a clinical response strongly suggests that combination immunotherapeutic approaches rather than monotherapy may be necessary to reverse the multifactorial mechanisms of immune suppression in myeloproliferative neoplasms. This trial was registered at www.clinicaltrials.gov as #NCT03065400.

Background: The COVID pandemic has resulted in significant changes many aspects of daily living. To understand the impact that COVID-19 has had on the myeloproliferative neoplasm (MPN) patient population, we conducted an internet based survey. Methods: Survey: This survey was hosted Mayo Clinic's secured REDCap system for online surveys with a link to the survey alongside a brief description posted via the www.mpnqol.com website, as well as other MPN organizational partners. Survey responses were completely anonymous. Questions included MPN-Total symptom score (TSS), NCCN distress thermometer (NCCN-DT), questions regarding impact on medical care, and questions from CDC COVID-19 community survey question bank regarding the impact of social distancing as well as changes in health behaviors. Distress thermometer, MPN-TSS, and/or questions related to the impact of COVID-19 on MPN treatment were analyzed by: MPN diagnosis, among those with ET, PV, or MF diagnoses; medication status; stay at home order; community spread; and country. Associations were tested using Kruskal-Wallis or Wilcoxon rank sum tests (for continuous variables) or Fisher Exact tests (for categorical variables). Analysis: Results: Patient Demographics (Table 1): 1560 people responded to the survey, 1217 were eligible for analysis. Median age was 62 (range: 21-93), and 298 (24.6%) respondents were male. There were respondents from USA, Australia, Canada, Netherlands, Ireland, and UK. 233 patients (19.2%) have myelofibrosis, 419 (34.6%) polycythemia vera and 543 (44.8%) essential thrombocythemia. At the time of the COVID outbreak, 1026 (84.3%) were on MPN directed medical therapy, including ruxolitinib (15.3%), interferon (14.7%), hydroxyurea (42.7%) and ASA (47.7%). 165 (13.6%) respondents received COVID testing, of which 5 had positive tests. Impact on MPN Care (Table 2): We sought to understand how patient's clinical care changed. Over half respondents who spoke to their MPN doctor had a telemedicine visit after COVID19 (57.1%). 422 (36.5%) patients spaced out visits, of which 99 (22.7%) felt there were consequences. A change in therapy due to COVID-1 occurred in only 5.4% of patients. MPN Symptom Burden and QoL: Data captured on the NCCN-DT had a median of 4 (0-10). MPN-SAF-TSS composite score was collected in 1150 respondents, median score was 26 (0-90). These scores are higher than those previously reported. Pandemic Impact on Lifestyle (Table 1): 595 (49.5%) of patients report living in a community where there is significant COVID-19 spread. 946 (78.9%) reported that COVID-19 has impacted their day to day life. 198 (17.2%) of patients agreed, or strongly agreed that COVID had a significant impact on their finances. 799 (67.8%) had a stay at home order. Of those who quarantined (112), the median duration was 30d (1-120). The majority of people increased hand-washing, and cleaning habits. 954 (81.7%) respondents reported wearing masks in public. 908 (76.8%) reported increased stress from social distancing. The majority of respondents report using healthy coping habits, such as reaching out to friends/loved ones, breathing and relaxation, as well as healthy diet. Less than 15% of patients report unhealthy coping strategies, such as use of opioids, benzodiazepines, alcohol, or cannabis Factors associated with response: There were no differences in responses based on type of MPN. If a patient was on medication, they were more likely to have spoken to their provider (p<0.001). If there was a stay at home order in place, there was a higher MPN-TSS score (p<0.001). If the respondent lived in an area of high community spread, they had a higher NCCN-DT score (p<0.001). Patients in the USA had a higher NCCN-DT score (p=0.001), were more likely to stretch out the duration of time between visits (p<0.001) and less likely to have a telemedicine visit (p<0.001). Although fewer respondents in the USA thought COVID-19 was a serious disease (p=0.02), a higher percentage of respondents wore masks (p <0.001). Conclusions: In our survey of MPN patients, there were many changes noted in clinical care. The use of telemedicine was common, and at least a third had significant changes in their care. Most experienced increased stress, however, employed healthy coping strategies. Only a minority of patients had a COVID test, and only 5 were positive, further data will be needed to understand the impact of COVID infection. Figure 1 Disclosures Harrison: Roche: Honoraria; Incyte Corporation: Speakers Bureau; Celgene: Honoraria, Research Funding, Speakers Bureau; Sierra Oncology: Honoraria; Promedior: Honoraria; Shire: Honoraria, Speakers Bureau; AOP Orphan Pharmaceuticals: Honoraria; Novartis: Honoraria, Research Funding, Speakers Bureau; Janssen: Speakers Bureau; Gilead Sciences: Honoraria, Speakers Bureau; CTI Biopharma Corp: Honoraria, Speakers Bureau. Pemmaraju:Affymetrix: Other: Grant Support, Research Funding; Plexxikon: Research Funding; Incyte Corporation: Honoraria; Roche Diagnostics: Honoraria; Blueprint Medicines: Honoraria; Novartis: Honoraria, Research Funding; SagerStrong Foundation: Other: Grant Support; DAVA Oncology: Honoraria; Samus Therapeutics: Research Funding; Cellectis: Research Funding; Daiichi Sankyo: Research Funding; Celgene: Honoraria; AbbVie: Honoraria, Research Funding; Stemline Therapeutics: Honoraria, Research Funding; MustangBio: Honoraria; LFB Biotechnologies: Honoraria; Pacylex Pharmaceuticals: Consultancy. Vannucchi:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees; Blueprint: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Gupta:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol MyersSquibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Research Funding; Pfizer: Consultancy. Mascarenhas:Celgene, Prelude, Galecto, Promedior, Geron, Constellation, and Incyte: Consultancy; Incyte, Kartos, Roche, Promedior, Merck, Merus, Arog, CTI Biopharma, Janssen, and PharmaEssentia: Other: Research funding (institution). Shimoda:Kyowa Hakko Kirin Co., Ltd.: Research Funding; Pfizer Inc.: Research Funding; Otsuka Pharmaceutical: Research Funding; Celgene: Honoraria; Perseus Proteomics: Research Funding; PharmaEssentia Japan: Research Funding; AbbVie Inc.: Research Funding; Astellas Pharma: Research Funding; Merck & Co.: Research Funding; CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Bristol-Myers Squibb: Honoraria; Takeda Pharmaceutical Company: Honoraria; Novartis: Honoraria, Research Funding; Shire plc: Honoraria; Asahi Kasei Medical: Research Funding; Japanese Society of Hematology: Research Funding; The Shinnihon Foundation of Advanced Medical Treatment Research: Research Funding. Kiladjian:AOP Orphan: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Komatsu:AbbVie: Other: member of safety assessment committee in M13-834 clinical trial.; Otsuka Pharmaceutical Co., Ltd., Shire Japan KK, Novartis Pharma KK, PharmaEssentia Japan KK, Fuso Pharmaceutical Industries, Ltd., Fujifilm Wako Pure Chemical Corporation, Chugai Pharmaceutical Co., Ltd., Kyowa Hakko Kirin Co., Ltd., Takeda Pharmaceutica: Research Funding; Meiji Seika Pharma Co., Ltd.: Patents & Royalties: PCT/JP2020/008434, Research Funding; PPMX: Consultancy, Research Funding; Otsuka Pharmaceutical Co., Ltd., PharmaEssentia Japan KK, AbbVie GK, Celgene KK, Novartis Pharma KK, Shire Japan KK, Japan Tobacco Inc: Consultancy; Takeda Pharmaceutical Co., Ltd, Novartis Pharma KK, Shire Japan KK: Speakers Bureau. Abello:Takeda: Honoraria, Research Funding; Novartis: Consultancy, Honoraria; Amgen: Consultancy, Research Funding; Dr. Reddy's: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding. Gomez-Almaguer:Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Scherber:Incyte Corporation: Current Employment, Current equity holder in publicly-traded company. Mauro:Novartis: Consultancy, Honoraria, Other: Travel, Accommodation, Expenses, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Other: Travel, Accommodation, Expenses, Research Funding; Sun Pharma/SPARC: Research Funding; Takeda: Consultancy, Honoraria, Other: Travel, Accommodation, Expenses, Research Funding; Pfizer: Consultancy, Honoraria, Other: Travel, Accommodation, Expenses, Research Funding. Mesa:Samus Therapeutics: Research Funding; Novartis: Consultancy; Genentech: Research Funding; Incyte: Research Funding; Bristol Myers Squibb: Research Funding; AbbVie: Research Funding; CTI BioPharma: Research Funding; Sierra Oncology: Consultancy; LaJolla Pharmaceutical Company: Consultancy; Promedior: Research Funding.

Background Activating mutations in JAK2 are the molecular hallmark of PV. However, achieving molecular remission is not a validated endpoint in PV, as its correlation with patient-relevant endpoints, such as thrombotic events or disease progression, is not well established. The expression of MDM2, a negative regulator of wild-type p53, is significantly higher in CD34+ cells from patients with PV vs those from healthy controls. Therefore, MDM2 antagonists such as idasanutlin (idasa) may have selective and potentially disease-modifying effects in PV. This exploratory analysis reports baseline mutational profiling and serial measurements of JAK2 V617F variant allele frequency (VAF) from patients treated with idasa in the Phase II NP39761 study (NCT03287245). Methods Patients with PV, as defined by the 2016 World Health Organization criteria, were eligible for inclusion if their disease was HU resistant/intolerant according to European LeukemiaNet criteria and they were phlebotomy dependent (≥ 1 phlebotomy in the 16-wk period prior to screening). Prior PV therapy with ruxolitinib and/or interferon was allowed. Idasa was given orally once daily on days 1-5 of 28-day cycles for up to 24 mo. The starting dose was 150 mg, but dose increase (to 200 mg) or decrease (to 100 mg) was allowed per protocol-defined criteria. The primary efficacy endpoints were hematocrit control (HTC), defined as maintaining acceptable hematocrit levels with ≤ 1 phlebotomy between cycle 1, day 1 (C1D1) and wk 8 and no phlebotomy after wk 8, and complete hematologic remission (CHR), defined as HTC together with platelets < 400 × 109/L and white blood cell count < 109/L on the day of response assessment (or most recent test). JAK2 V617F VAF was analyzed at screening and at C3D28, C5D28 and wk 32. The JAK2 V617F VAF was determined using quantitative polymerase chain reaction. Baseline blood samples were sequenced using the Foundation Medicine FoundationOne Heme next-generation sequencing panel, which interrogates > 400 DNA-sequenced genes, to explore the genetic landscape of PV beyond JAK2 V617F. Results All 27 patients enrolled in the study harbored JAK2 V617F. Baseline and ≥ 1 later JAK2 VAF measurements were available in 23 patients, allowing for analysis. The median age was 56 y (range, 34-74), and 7 patients (26%) had been previously treated with ruxolitinib. Median treatment duration was 257 days (range, 5-677), and the median number of treatment cycles was 8 (range, 1-22). JAK2 V617F VAFs at baseline were highly variable, ranging from 7% to 96% (median, 66%). A reduction in JAK2 V617F VAF was observed as early as after 3 cycles (median reduction, 39%; n = 19) and was sustained in patients receiving treatment, with a median reduction of 58% at C5D28 (n = 17) and of 76% at wk 32 (n = 13). The median reductions in JAK2 V617F VAF were significantly higher for patients with CHR and HTC than in nonresponders on C3D28 (CHR, P < 0.01; HTC, P = 0.04) and C5D28 (CHR, P < 0.01; HTC, P = 0.03), with a similar trend also at wk 32 (CHR, P = 0.06; HTC, P = 0.19) (Figures). Baseline targeted sequencing (n = 16) identified several additional subclonal mutations. However, no TP53 mutations were detected. Variants in TET2 and ASXL1 were detected in 37% (6 of 16) and 20% (3 of 16) of patients, with VAFs of 2%-51% and 38%-50%, respectively. Notably, 68% of the patients had variants detected in 1 to 3 DNA repair genes, including ATM (VAF, 47%-52%), ATR (VAF, 49%), BRCA2 (VAF, 47%-51%), PARP1 (VAF, 52%), PARP3 (VAF, 48%), FANCM (VAF, 47%-50%), BLM (VAF, 48%) and MSH3 (VAF, 49%). In the absence of sequencing of patient-matched non-hematologic tissue and the VAFs being ≈50%, it is possible some of these variants are germline. Whether such variants predispose to PV is unknown. Conclusions Idasa has relevant clinical activity in patients with PV who are resistant to or intolerant of HU and showed rapid JAK2 V617F VAF reduction in a subset of patients as early as after 3 treatment cycles. The median JAK2 VAF reduction was significantly greater in patients who achieved CHR and HTC after 3 and 5 cycles of idasa treatment, suggesting that early molecular response was associated with higher likelihood of clinical response. Baseline mutations were seen in several genes commonly mutated in PV. A high frequency of variants in DNA repair genes has not previously been reported in PV and may contribute to genomic instability in this disease. Figure Disclosures Passamonti: Roche: Other: Support of parent study and funding of editorial support; BMS: Speakers Bureau; Novartis: Speakers Bureau. El-Galaly:F. Hoffmann-La Roche: Current Employment, Other: Support of parent study and funding of editorial support. Gerds:Celgene: Consultancy, Research Funding; Gilead Sciences: Research Funding; CTI Biopharma: Consultancy, Research Funding; Imago Biosciences: Research Funding; AstraZeneca/MedImmune: Consultancy; Roche/Genentech: Research Funding; Incyte Corporation: Consultancy, Research Funding; Pfizer: Research Funding; Apexx Oncology: Consultancy; Sierra Oncology: Research Funding. Gupta:Incyte: Honoraria, Research Funding; Bristol MyersSquibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy. Higgins:Roche: Current Employment, Current equity holder in publicly-traded company, Other: Support of parent study and funding of editorial support. Huw:Roche: Current Employment, Other: Support of parent study and funding of editorial support. Maffioli:Roche: Other: Support of parent study and funding of editorial support. Mesa:Sierra Oncology: Consultancy; Incyte: Research Funding; Samus Therapeutics: Research Funding; Promedior: Research Funding; Genentech: Research Funding; Novartis: Consultancy; CTI BioPharma: Research Funding; LaJolla Pharmaceutical Company: Consultancy; AbbVie: Research Funding; Bristol Myers Squibb: Research Funding. Rambaldi:Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Support of parent study and funding of editorial support. Received travel support., Research Funding; Sanofi: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Astellas: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support from Gilead.; BMS/Celgene: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Advisory board and speaker fees from Pfizer.; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Research grant from Amgen Inc.; Omeros: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); University of Milan: Current Employment. Vannucchi:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees; Blueprint: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Yacoub:Incyte: Speakers Bureau; Hylapharm: Current equity holder in private company; Cara Therapeutics: Current equity holder in publicly-traded company; Dynavax: Current equity holder in publicly-traded company; Agios: Honoraria, Speakers Bureau; Novartis: Speakers Bureau; Roche: Other: Support of parent study and funding of editorial support; Ardelyx: Current equity holder in publicly-traded company. Mascarenhas:Celgene, Prelude, Galecto, Promedior, Geron, Constellation, and Incyte: Consultancy; Incyte, Kartos, Roche, Promedior, Merck, Merus, Arog, CTI Biopharma, Janssen, and PharmaEssentia: Other: Research funding (institution).

Myelofibrosis (MF) is characterized by progressive bone marrow (BM) fibrosis resulting from aberrant megakaryopoeisis and expression of pro-inflammatory cytokines. These two processes, heavily influenced by bromodomain and extraterminal domain (BET)-mediated gene regulation, lead to myeloproliferation and cytopenias. CPI-0610 is a potent, selective and unique BET inhibitor under investigation in MF patients as monotherapy or in combination with ruxolitinib in the MANIFEST trial (NCT02158858). In ruxolitinib naïve and experienced MF patients, treatment with CPI-0610 monotherapy or in combination with ruxolitinib not only reduced spleen volume and symptoms, but also improved hemoglobin levels and overcame transfusion dependency in a subset of patients. To evaluate the effects of CPI-0610 on BM biology, correlative analyses were conducted using patient samples collected from the MANIFEST trial. Pre-treatment and post-treatment BM biopsy samples were available from 78 evaluable patients, with reticulin staining conducted and evaluated by local pathologists available for 34 pre-treatment and 24-week post-treatment pairs of BM biopsy samples. Improvement in reticulin staining of at least one grade was observed in 32% (11/34) of patients. Central pathology review of reticulin staining is ongoing and will be presented. Additional bone marrow biopsy pairs collected pre-treatment and 24-week post-treatment for exploratory histopathological assessments were available from a total of 23 unselected MANIFEST patients at the time of the abstract submission. To assess changes in erythroid and megakaryocytic lineages, H&E and immunohistochemistry (IHC) staining of CD71 and CD61 were conducted centrally. Semi-quantitative analysis revealed an overt increase in erythroid lineage formation in 61% (14/23) of patients. Patients with CD71 improvement in BM IHC generally showed a greater increase in median hemoglobin levels than those without improvement. Tight clusters of megakaryocytes (MK), characteristic in MF BM, were observed at baseline in all cases and were decreased/absent after treatment in 52% (12/23) patients. In addition, decreased MK number to <5/high powered field was also observed in 39% (9/23) of patients. Overall improvement in MK histotopography was observed in 65% of patients (15/23). Central histopathology review with IHC staining, including reticulin staining, will be conducted on additional samples and will be available for presentation at the conference. To further dissect the underlying mechanism of these relative improvements in bone marrow composition and histotopography induced by CPI-0610, CD34+ hematopoietic stem cells were isolated from peripheral blood collected from multiple MF patients at baseline to evaluate the impact of CPI-0610 on MK and erythroid differentiation in vitro. When CD34+ cells from MF patients were treated with CPI-0610 in erythroid differentiation conditions in the presence of SCF, IL3 and EPO, a dose-dependent increase in more mature erythroid cell populations was observed. However, under the same conditions, ruxolitinib suppressed erythroid differentiation, which is consistent with ruxolitinib inhibition of EPO signaling and the anemia caused by ruxolitinib treatment in MF patients. Suppressive effects of ruxolitinib on erythroid differentiation were partially rescued by CPI-0610 in a dose-dependent manner. CPI-0610 treatment of CD34+ cells from MF patients in MK differentiating conditions in the presence of SCF, IL6, IL9 and TPO resulted in a dose-dependent decrease in proliferation of CD34+ cells and an increase in the ratio of late MK (CD34-/CD41a+/CD42b+) and early MK (CD34+/CD41a+/CD42b+). This CPI-0610-induced dose-dependent maturation of aberrant immature MK cells may play a role in reducing MF disease manifestations. Molecular studies to further our understanding of the underlying mechanisms of CPI-0610 treatment are ongoing. Taken together, these paired BM biopsy and in vitro myeloid maturation results demonstrated an effect of CPI-0610 in promoting erythroid and MK differentiation. These results may partially explain CPI-0610's clinical effects in MF patients, including rising hemoglobin, reduced transfusion dependency and reduction in spleen volume and symptoms. Disclosures Mertz: Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Keller:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Meyer:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Zavidij:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Cui:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Verstovsek:Roche: Research Funding; Gilead: Research Funding; Promedior: Research Funding; Sierra Oncology: Consultancy, Research Funding; Protagonist Therapeutics: Research Funding; AstraZeneca: Research Funding; Genentech: Research Funding; Novartis: Consultancy, Research Funding; Blueprint Medicines Corp: Research Funding; Celgene: Consultancy, Research Funding; CTI Biopharma Corp: Research Funding; PharmaEssentia: Research Funding; Incyte Corporation: Consultancy, Research Funding; ItalPharma: Research Funding; NS Pharma: Research Funding. Gupta:Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol MyersSquibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Incyte: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Talpaz:IMAGO: Consultancy; Takeda: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Constellation Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Novartis: Research Funding. Harrison:Promedior: Honoraria; AOP Orphan Pharmaceuticals: Honoraria; Roche: Honoraria; Incyte Corporation: Speakers Bureau; Gilead Sciences: Honoraria, Speakers Bureau; CTI Biopharma Corp: Honoraria, Speakers Bureau; Shire: Honoraria, Speakers Bureau; Janssen: Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Research Funding, Speakers Bureau; Sierra Oncology: Honoraria. Mead:CTI: Consultancy; Gilead: Consultancy; Novartis: Consultancy, Honoraria, Other: travel, accommodations, expenses, Research Funding, Speakers Bureau; Celgene/BMS: Consultancy, Honoraria, Other: travel, accommodations, expenses, Research Funding; Abbvie: Consultancy. Mesa:Novartis: Consultancy; CTI BioPharma: Research Funding; Bristol Myers Squibb: Research Funding; Sierra Oncology: Consultancy; Genentech: Research Funding; Samus Therapeutics: Research Funding; LaJolla Pharmaceutical Company: Consultancy; Incyte: Research Funding; Promedior: Research Funding; AbbVie: Research Funding. Mascarenhas:Celgene, Prelude, Galecto, Promedior, Geron, Constellation, and Incyte: Consultancy; Incyte, Kartos, Roche, Promedior, Merck, Merus, Arog, CTI Biopharma, Janssen, and PharmaEssentia: Other: Research funding (institution). Senderowicz:Constellation Pharmaceuticals: Consultancy, Current equity holder in publicly-traded company, Ended employment in the past 24 months; Puma Biotechnology: Membership on an entity's Board of Directors or advisory committees. Colak:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Shao:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Luptakova:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Humphrey:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Wang:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Trojer:Constellation Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company.

Background PV is a clonal myeloid neoplasm characterized by activating mutations in JAK2 and increased red blood cell production. Reduction of thrombosis risk through lowering of hematocrit (Hct) and thus blood viscosity is critical, but management of constitutional symptoms is also important. HU is an effective and well-tolerated first-line treatment (tx) for PV, but pts who develop resistance to or intolerance of HU have limited tx options. A Phase I study of idasanutlin, an MDM2 antagonist leading to increased p53 activity, showed encouraging efficacy and potential disease-modifying effects via rapid reduction in JAK2 V617F variant allele frequency in 11 pts with PV. These results prompted the larger, international Phase II study of idasanutlin in HU-resistant/intolerant PV (NCT03287245); data from the initial phase of the study are reported here. Methods Pts meeting the 2016 WHO criteria for PV were eligible for inclusion if they had HU-resistant/intolerant disease according to the European LeukemiaNet (ELN) criteria and were phlebotomy dependent (≥ 1 phlebotomy in the 16-wk period prior to screening). Prior PV tx with ruxolitinib (rux) or interferon was allowed. Idasanutlin was given orally once daily on days 1-5 of 28-day cycles for up to 24 mo. The starting dose was 150 mg; increase to 200 mg was allowed for non-responders at cycle 3, day 28, and reduction to 100 mg was permitted for toxicity and for pts treated beyond cycle 12. Antiemetic prophylaxis was mandatory in cycle 1 throughout the study and later became mandatory in all cycles. The primary endpoint (wk 32) was the composite response of Hct control (HTC) and spleen volume reduction > 35% by CT/MRI in pts with splenomegaly (> 450 cm3) and HTC alone in pts without splenomegaly. Key secondary endpoints included safety, complete hematologic response (CHR; defined as HTC and normalization of platelets/leukocytes) and ELN response. Results A total of 27 pts were included in this study and received tx with idasanutlin. Median age was 56 years (range, 34-74) and 16 pts (59.3%) were male (Table 1). All pts had JAK2 V617F mutation; 7 had previous exposure to rux. Median tx duration was 257 days (range, 5-677); the median number of treatment cycles was 8 (range, 1-23). Dose modifications occurred in 17 pts (63.0%; Table 2). A total of 3 serious AEs occurred: atrial flutter, atrial fibrillation and nausea/vomiting (n = 1 each). The serious cardiac AEs occurred in pts with pre-existing hypertension and a past incident of heart failure not symptomatic upon enrollment, respectively. No deaths, transformation to acute myeloid leukemia, progression to myelofibrosis or thrombotic events occurred during the study. AEs occurring in ≥ 15% of pts are listed in Table 3; gastrointestinal toxicity and fatigue were the most common events. The population for primary endpoint evaluation consisted of pts with response assessed at wk 32 (n = 16). One of 13 pts with baseline splenomegaly achieved a composite response (7.7%; Table 4). Nine of 16 pts (56.3%) among all evaluable pts achieved HTC: 6 of 11 rux-naive pts (54.5%) and 3 of 5 rux-exposed pts (60.0%). Eight of 13 pts (61.5%) among all pts had HTC duration ≥ 12 wk beyond wk 32: 5 of 9 rux-naive pts (55.6%) and 3 of 4 rux-exposed pts (75.0%). At wk 32, 8 of 16 pts (50.0%) achieved a CHR, with 6 of 13 (46.2%) having a CHR duration ≥ 12 wk beyond wk 32. Overall response rates per modified ELN response criteria in pts with baseline splenomegaly, pts without baseline splenomegaly and in all pts were 69.2% (9 of 13), 66.7% (2 of 3) and 68.8% (11 of 16), respectively; 9 of 15 pts (60%) among all pts had a response duration ≥ 12 wk beyond wk 32. Median (range) laboratory value changes at wk 32 were: platelets, −253 × 109/L (−2083 to +175) and leukocytes, −4.8 × 109/L (−25.3 to +3.4). At wk 32, 6 of 14 pts (42.9%) had a ≥ 50% reduction in the Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score. Conclusions Idasanutlin showed relevant clinical activity in pts with HU-resistant/intolerant PV and also in a subset of pts with prior rux tx. However, the low-grade gastrointestinal toxicity profile of idasanutlin was not effectively mitigated with antiemetic prophylaxis and led to frequent discontinuations. These results iterate the importance of tolerability of novel therapies administered over the long term for pts with PV. Disclosures Mascarenhas: Celgene, Prelude, Galecto, Promedior, Geron, Constellation, and Incyte: Consultancy; Incyte, Kartos, Roche, Promedior, Merck, Merus, Arog, CTI Biopharma, Janssen, and PharmaEssentia: Other: Research funding (institution). Higgins:Roche: Current Employment, Current equity holder in publicly-traded company, Other: Support of parent study and funding of editorial support. Anders:Roche: Current Employment, Other: Support of parent study and funding of editorial support. Burbury:Roche: Other: Support of parent study and funding of editorial support. El-Galaly:F. Hoffmann-La Roche: Current Employment, Other: Support of parent study and funding of editorial support. Gerds:Roche/Genentech: Research Funding; Apexx Oncology: Consultancy; AstraZeneca/MedImmune: Consultancy; Pfizer: Research Funding; Imago Biosciences: Research Funding; Gilead Sciences: Research Funding; Incyte Corporation: Consultancy, Research Funding; Sierra Oncology: Research Funding; CTI Biopharma: Consultancy, Research Funding; Celgene: Consultancy, Research Funding. Gupta:Pfizer: Consultancy; Incyte: Honoraria, Research Funding; Bristol MyersSquibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Kovic:Roche: Other: Support of parent study and funding of editorial support. Maffioli:Roche: Other: Support of parent study and funding of editorial support. Mesa:AbbVie: Research Funding; Sierra Oncology: Consultancy; CTI BioPharma: Research Funding; LaJolla Pharmaceutical Company: Consultancy; Bristol Myers Squibb: Research Funding; Genentech: Research Funding; Samus Therapeutics: Research Funding; Promedior: Research Funding; Novartis: Consultancy; Incyte: Research Funding. Rambaldi:Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Support of parent study and funding of editorial support. Received travel support., Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Advisory board and speaker fees from Pfizer.; Sanofi: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); BMS/Celgene: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); University of Milan: Current Employment; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support from Gilead.; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Omeros: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Astellas: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Research grant from Amgen Inc.. Vannucchi:AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Blueprint: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Yacoub:Roche: Other: Support of parent study and funding of editorial support; Dynavax: Current equity holder in publicly-traded company; Novartis: Speakers Bureau; Agios: Honoraria, Speakers Bureau; Incyte: Speakers Bureau; Hylapharm: Current equity holder in private company; Cara Therapeutics: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company.

Abstract PAC203 is a randomized dose-finding study of pacritinib, an oral JAK2/IRAK1 inhibitor, in patients with advanced myelofibrosis who are intolerant of or resistant to ruxolitinib. Patients were randomized 1:1:1 to pacritinib 100 mg once per day, 100 mg twice per day, or 200 mg twice per day. Enhanced eligibility criteria, monitoring, and dose modifications were implemented to mitigate risk of cardiac and hemorrhagic events. Efficacy was based on ≥35% spleen volume response (SVR) and ≥50% reduction in the 7-component total symptom score (TSS) through week 24. Of 161 patients, 73% were intolerant of and 76% had become resistant to ruxolitinib; 50% met criteria for both. Severe thrombocytopenia (platelet count <50 × 103/μL) was present in 44%. SVR rates were highest with 200 mg twice per day (100 mg once per day, 0%; 100 mg twice per day, 1.8%; 200 mg twice per day, 9.3%), particularly among patients with baseline platelet counts <50 × 103/μL (17%; 4 of 24). Although TSS response rate was similar across doses (100 mg once per day, 7.7%; 100 mg twice per day, 7.3%; 200 mg twice per day, 7.4%), median percent reduction in TSS suggested a dose-response relationship (–3%, −16%, and −27%, respectively). Pharmacokinetic and pharmacodynamic modeling based on all available data showed greatest SVR and TSS reduction at 200 mg twice per day compared with lower doses. Common adverse events were gastrointestinal events, thrombocytopenia, and anemia. There was no excess of grade ≥3 hemorrhagic or cardiac events at 200 mg twice per day. Pacritinib 200 mg twice per day demonstrated clinical activity and an acceptable safety profile and was selected as the recommended dose for a pivotal phase 3 study in patients with myelofibrosis and severe thrombocytopenia. This trial was registered at www.clinicaltrials.gov as #NCT03165734.

AbstractActivation of the P53 pathway through inhibition of MDM2 using nutlins has shown clinical promise in the treatment of solid tumors and hematologic malignancies. There is concern, however, that nutlin therapy might stimulate the emergence or expansion of TP53-mutated subclones. We recently published the results of a phase 1 trial of idasanutlin in patients with polycythemia vera (PV) that revealed tolerability and clinical activity. Here, we present data indicating that idasanutlin therapy is associated with expansion of TP53 mutant subclones. End-of-study sequencing of patients found that 5 patients in this trial harbored 12 TP53 mutations; however, only 1 patient had been previously identified as having a TP53 mutation at baseline. To identify the origin of these mutations, further analysis of raw sequencing data of baseline samples was performed and revealed that a subset of these mutations was present at baseline and expanded during treatment with idasanutlin. Follow-up samples were obtained from 4 of 5 patients in this cohort, and we observed that after cessation of idasanutlin, the variant allele frequency (VAF) of 8 of 9 TP53 mutations decreased. Furthermore, disease progression to myelofibrosis or myeloproliferative neoplasm blast phase was not observed in any of these patients after 19- to 32-month observation. These data suggest that idasanutlin treatment may promote transient TP53 mutant clonal expansion. A larger study geared toward high-resolution detection of low VAF mutations is required to explore whether patients acquire de novo TP53 mutations after idasanutlin therapy.

Introduction: FDA approval of JAK2-inhibitors for myelofibrosis (MF) has changed the landscape for treatment introducing possible increased complexity of clinical trial designs in MF. Many patients with MF will have insufficient response or intolerance to ruxolitinib, opening an opportunity for testing of novel agents alone or in combination. Novel trial designs exist for early stage (phase 1 and 2) studies. The Myeloproliferative Neoplasms Research Consortium (MPN-RC) is an NCI-funded academic group of laboratory and clinical scientists working to develop and evaluate treatments that will improve the survival of patients with MPNs focused on early stage trials in MF. This review was undertaken to understand the landscape of MF clinical trials and improve our approach to trial design. Methods: Studies with "myelofibrosis" as a condition were abstracted from clinicaltrials.gov using an application programming interface from 2010-2019 and reviewed for phase, trial design features, and endpoints. Trial design review captured such features as presence of dose escalation and approach (rule-based versus model-based/assisted) in the phase 1 setting. Observational and behavioral based studies were excluded. A total of 165 treatment interventional studies including MF patients (either MF as the primary cohort, or MF along with other MPN, myelodysplastic syndrome, or hematologic malignancies related cohorts) were reviewed. Primary and secondary endpoints were reviewed for quality of life, symptoms, or other patient-reported outcomes (PRO). Results: A median of 16.5 (range 13-20) trials were initiated per year; 92 (56%) phase 2, 54 (33%) phase 1; 17 (10%) phase 3 and 2 (1%) phase 4, with 77 (47%) industry sponsored (Figure 1). Among phase 1 trials, 41/54 (76%) included dose escalation, the majority employing a standard 3+3 design (or other rule-based design) or not specifically detailing the dose escalation schema. Less than 5 dose escalation trials were explicitly described as model-based or model-assisted. Almost half of the phase 1 trials (23/54; 43%) included combination treatment, with 17/23 (74%) using ruxolitinib or fedratinib. Among phase 2 trials, 82 (89%) were non-randomized and 10 (11%) randomized trials; 35/92 (38%) involved combination treatment and 57 (62%) single agent. Median actual/target enrollment for the phase 3 trials (n=16) was 192 patients (range 49-2233 patients); only 2 phase 3 trials were > 500 patients. Median number of total outcomes was 6.0 (range 1-28) across all studies with a median of 5.5 (range 1-28) for 2010-2014 versus 7.0 (range 1-22) for 2015-2019 (p=0.09). Overall 63/165 (38%) studies included at least one PRO endpoint; 15 (28%) phase 1, 33 (36%) phase 2 and 14 (82%) phase 3. Inclusion of PRO endpoints for years 2010-2014 was similar to studies started in years 2015-2019 [31/82 (38%) and 32/83 (39%)]. Industry sponsored studies included PRO endpoints more frequently [46/77 (60%) versus 17/88 (19%); p<0.001] than non-industry sponsored trials but this is primarily due to a higher proportion of phase 3/4 trials (n=17) being conducted by industry versus non-industry (n=2) (Figure 2). Conclusions: For phase 1 trials in MF, few dose-escalation trials included model-based or model-assisted methods. These designs are encouraged in order to maximize therapeutic benefits in MF, a rare cancer. Clinical trial designs in myelofibrosis have shifted in recent years as evidenced by an increase in number of endpoints, likely to accommodate new challenges in the post JAK2-inhibitors approval era. Use of patient-reported outcomes including quality of life and symptom assessment was high in the phase 3 setting, and continued use should be encouraged as endpoint assessments in MF clinical trial designs. Disclosures Mascarenhas: Celgene, Prelude, Galecto, Promedior, Geron, Constellation, and Incyte: Consultancy; Incyte, Kartos, Roche, Promedior, Merck, Merus, Arog, CTI Biopharma, Janssen, and PharmaEssentia: Other: Research funding (institution). Mesa:LaJolla Pharma: Consultancy; Novartis: Consultancy; Sierra Onc: Consultancy; Abbvie: Research Funding; Celgene: Research Funding; CTI: Research Funding; Genetech: Research Funding; Incyte: Research Funding; Promedior: Research Funding; Samus: Research Funding. Hoffman:Dompe: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Forbius: Consultancy; Protagonist: Consultancy.

Introduction Essential thrombocythemia (ET) and polycythemia vera (PV) patients suffer from various symptoms that worsen quality of life (QOL), yet serial data on symptom changes resulting from therapy are sparse in the literature. Patient questionnaires from 2 large multicenter trials (MPN-RC 111, 112) were used to assess change in symptom burden and QOL over 12 months and impact of baseline symptom burden on subsequent change in ET / PV patients on hydroxyurea (HU) or pegylated interferon alfa-2a (PEG). Methods Trials MPN-RC 111 was a single-arm, open-label, phase II trial evaluating response to PEG in high-risk ET / PV patients with HU resistance/intolerance or splanchnic vein thrombosis (SVT; NCT01259817). MPN-RC 112 was a randomized, open-label, phase III trial comparing response to PEG versus HU in cytoreductive therapy naïve high-risk ET / PV patients diagnosed < 5 years ago (NCT01258856). Measures Patients reported disease-related symptoms via the validated Myeloproliferative Neoplasms Symptom Assessment Form (MPN-SAF), QOL via the European Organisation for the Research and Treatment of Cancer Core QOL Questionnaire (EORTC QLQ-C30), and (if applicable) PEG-related symptoms (flu-like symptoms, injection site irritation, blurry vision, vision change, flushing) at baseline, 3, 6, 9, and 12 months. Analysis Mixed models assessed mean changes from baseline in the MPN-SAF Total Symptom Score (TSS), MPN-SAF items, QOL, and PEG-related symptoms in MPN-RC 111, 112 PEG, and 112 HU patients. Mixed models also assessed the impact of baseline symptom burden (high [TSS ≥ 20] versus low) on subsequent change in PEG (MPN-RC 111 and 112) and HU patients. Results Patients Of the 135 enrolled MPN-RC 111 patients, 20 with SVT and 1 with no questionnaires were excluded. Of the remaining 114, 64 (56%) / 50 (44%) had ET / PV. Patients were 51% / 48% female. Median age was 65 / 64 years, and median time since diagnosis was 38 / 55 months. 31% / 22% had prior thrombosis, and 19% / 56% had splenomegaly. Of the 168 enrolled MPN-RC 112 patients (82 PEG, 86 HU), 2 with no questionnaires were excluded. Of the remaining 166, 79 (48%) / 87 (52%) had ET / PV. Patients were 50% / 33% female. Median age was 60 / 62 years, and median time since diagnosis was 3 / 3 months. 25% / 29% had prior thrombosis, and 11% / 37% had splenomegaly. Symptoms Questionnaire completion rates ranged from 90 - 99%, 87 - 100%, and 75 - 96% for on-treatment MPN-RC 111, 112 PEG, and 112 HU patients. At baseline, TSS (0 [absent] - 100 [worst imaginable]) and QOL (0 [very poor] - 100 [excellent]) means (SDs) were 19.5 (18.4) and 71.6 (20.1) for MPN-RC 111, 17.0 (13.6) and 67.9 (24.3) for MPN-RC 112 PEG, and 14.6 (11.4) and 73.8 (18.8) for MPN-RC 112 HU patients. On average, MPN-RC 111 patients had significant improvement of TSS, fatigue, abdominal pain, abdominal discomfort, dizziness, numbness, night sweats, and fever; MPN-RC 112 PEG patients had significant worsening of fever; and MPN-RC 112 HU patients had significant worsening of inactivity (no mean changes indicating improvement were observed). PEG patients had significant worsening of PEG-related symptoms. The greatest improvements occurred in the 46 (40%), 27 (33%), and 23 (28%) MPN-RC 111, 112 PEG, and 112 HU patients with high baseline symptom burden. On average, PEG patients with high baseline symptom burden had significant improvement of TSS, fatigue, early satiety, abdominal pain, abdominal discomfort, inactivity, headache, concentration, dizziness, numbness, insomnia, cough, night sweats, itching, bone pain, fever, weight loss, and QOL, while those with low baseline symptom burden had significant worsening of TSS, early satiety, headache, itching, and bone pain. On average, HU patients with high baseline symptom burden had significant improvement of TSS, early satiety, abdominal discomfort, headache, dizziness, numbness, insomnia, itching, and weight loss, while those with low baseline symptom burden had significant worsening of TSS, early satiety, abdominal discomfort, inactivity, concentration, and sexual desire/function (Figures 1 and 2). Conclusions Although no statistical comparisons were made across trials, overall improvements were seen in MPN-RC 111 but not 112. Patients with high baseline symptom burden experienced the greatest improvements in symptom burden and QOL during treatment with PEG or HU, which may explain the improvements seen in the more advanced patients in MPN-RC 111 compared to 112. Disclosures Mascarenhas: Celgene, Prelude, Galecto, Promedior, Geron, Constellation, and Incyte: Consultancy; Incyte, Kartos, Roche, Promedior, Merck, Merus, Arog, CTI Biopharma, Janssen, and PharmaEssentia: Other: Research funding (institution). Yacoub:Dynavax: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company; Cara Therapeutics: Current equity holder in publicly-traded company; Hylapharm: Current equity holder in private company; Incyte: Speakers Bureau; Agios: Honoraria, Speakers Bureau; Novartis: Speakers Bureau; Roche: Other: Support of parent study and funding of editorial support. Hoffman:Protagonist: Consultancy; Forbius: Consultancy; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Dompe: Research Funding. Silver:PharmaEssentia: Speakers Bureau. Mesa:Bristol Myers Squibb: Research Funding; Incyte: Research Funding; AbbVie: Research Funding; Samus Therapeutics: Research Funding; Genentech: Research Funding; CTI BioPharma: Research Funding; Promedior: Research Funding; Sierra Oncology: Consultancy; LaJolla Pharmaceutical Company: Consultancy; Novartis: Consultancy.