Carraway, Hetty E.

Abstract Background: Clonal cytopenia of undetermined significance (CCUS) is defined as persistent unexplained cytopenia with evidence of clonality [myeloid-associated somatic mutations (MTs) or cytogenetic [CG] abnormalities] but without definitive evidence of myeloid neoplasms (MN). The outcomes in CCUS patients (pts) are not well understood. Methods: The CCUS International Study database includes pts from 17 institutions who meet the criteria of CCUS and do not have other causes of cytopenia. Pts with MDS defining CG abnormalities were excluded. We collected baseline clinical data, laboratory parameters, CGs, molecular genetics, treatment, and disease course. Diverse gene panels from different institutions were collated to include a total of 70 myeloid-related somatic genes (30 genes in common). 2018 IWG MDS response criteria were used to determine response rate (RR). Disease progression (DP) is defined by progression to MN. The relationship between independent variables and DP and death was assessed using Cox proportional hazards models. Progression-free survival (PFS) and overall survival (OS) were estimated using Kaplan-Meier method. All statistical analysis was performed using SAS. Results: A total of 258 pts were captured by July 2021. The median age was 71 (IQR 63-77) years, and 66% were male. Among 73 (28%) pts with known malignancy history, 27 (37%) pts received previous chemo- or radiation therapy. 27 (10%) pts had non-malignant hematology comorbidities. 91 (35%) had cardiovascular disease, and 33 (13%) had inflammatory disease. (Table 1) The red blood cell and platelet transfusion-dependent rates were 7.3% and 2.3%, respectively. The median number of MTs was 2 (IQR 1-3), with 221 (86%) pts had ≥1 MT, of which 116 (53%) had ≥ 2 MTs. The most common 5 MTs were TET2 (n=78, 30%), SRSF2 (n=50, 19%), DNMT3A (n=47, 18%), ASXL1 (n=40, 16%), and U2AF1 (n=22, 9%) (Figure 1). The median VAF (mVAF) was 28% (IQR: 9.2%, 43%) with VAF < 10% in 47 (18%) and VAF ≥40% in 78 (30.2%) of the MTs. mVAF of the all genes are shown in Figure 2. Among pts with CG abnormalities (n=62, 24%), trisomy 8 and -Y are the most common karyotypes (n=15 for each, 24%) (Table 2). Eighty one (31%) patients received various treatments for CCUS with modest RR, including growth factors (n=47, 18.2%, RR: 25.5%), supportive care (n=23, 9%, RR: 26%), immunoglobulin/immunosuppressive therapy (n=15, 6%, RR: 40%), and DNMTi (n=8, 3%, RR=13%). The median length of follow-up was 15.6 (IQR 6.9-30.6) months. 24 pts progressed to MN, 14 (58.3%) of which were MDS, 8 (33.3%) CMML, and 2 (8.3%) AML. The 2-year PFS was 86.1% (95% CI: 80-93%) with a median PFS of 16.3 (IQR: 3.7, 21) months. In the multivariable model, positive MT of KRAS (HR: 8.4, 95% CI: 1.9-36.9, p=0.005) and CBL (HR: 16.5, 95% CI: 3.7-73.8, p=0.003) were significantly associated with DP. In the functional pathway analysis, having at least 1 splicing factor MT was significantly associated with DP (HR: 2.6, 95% CI:1.2-5.9, p=0.02). TP53 was not significantly associated with DP (HR: 1.2, 95% CI: 0.2-8.7, p=0.88). Having >1 MT (HR: 3.57, 95% CI: 1.19-10.7, p=0.02) compared to a single MT was significantly associated with DP (Figure 3). Over the follow-up period, 35 pts died. The 2-year OS was 81% (95% CI: 74.9-87.9%). In the multivariable model, MT of KRAS (HR: 6.1, 95% CI: 1.8-20, p=0.003), CBL (HR: 7.3, 95% CI: 1.7-31, p=0.007), and FLT3 (HR: 19.9, 95% CI: 2.5-155, p=0.004) were significantly associated with inferior survival. In the functional pathway analysis, MTs in activated signaling pathway were significantly associated with death (HR: 4.1, 95% CI: 1.8-9, p<0.001). None of the pts with TP53 MT died. Having >1 MT was not statistically significantly associated with higher risk of death (HR: 1.5, 95% CI: 0.7-3.0, p=0.28) (Figure 4). After adjustment for co-MT status and comorbidities, baseline Hb<10 g/dL (HR: 3.7, 95% CI: 1.8-7.9, p<0.001) was significantly associated with greater mortality. Conclusion: This large retrospective study summarizes the CCUS pts' characteristics, with different MT patterns and VAF. We confirmed the impact of having >1 MT on DP, but not OS. Genes involved in activated signaling had a significant impact on both DP and OS. TP53 MT was not associated with worse outcome. Findings may be due to limited cases in the particular genes and different gene panels from multiple institutions. A longer follow-up is planned to further describe the predictors for outcome in this ongoing study. Figure 1 Figure 1. Disclosures Komrokji: Jazz: Consultancy, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BMSCelgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Acceleron: Consultancy; PharmaEssentia: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Taiho Oncology: Membership on an entity's Board of Directors or advisory committees; Geron: Consultancy. Zeidan: BioCryst: Other: Clinical Trial Committees; Kura: Consultancy, Other: Clinical Trial Committees; Ionis: Consultancy; Geron: Other: Clinical Trial Committees; Incyte: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Boehringer Ingelheim: Consultancy, Research Funding; Novartis: Consultancy, Other: Clinical Trial Committees, Travel support, Research Funding; Janssen: Consultancy; Cardiff Oncology: Consultancy, Other: Travel support, Research Funding; Loxo Oncology: Consultancy, Other: Clinical Trial Committees; Aprea: Consultancy, Research Funding; AstraZeneca: Consultancy; Agios: Consultancy; BeyondSpring: Consultancy; Gilead: Consultancy, Other: Clinical Trial Committees; Daiichi Sankyo: Consultancy; Jazz: Consultancy; Astex: Research Funding; BMS: Consultancy, Other: Clinical Trial Committees, Research Funding; Acceleron: Consultancy, Research Funding; Pfizer: Other: Travel support, Research Funding; Genentech: Consultancy; Epizyme: Consultancy; Jasper: Consultancy; Astellas: Consultancy; ADC Therapeutics: Research Funding; AbbVie: Consultancy, Other: Clinical Trial Committees, Research Funding. Madanat: Blue Print Pharmaceutical: Honoraria; Stem line pharmaceutical: Honoraria; Onc Live: Honoraria; Geron Pharmaceutical: Consultancy. Coombs: LOXO: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria; AstraZeneca: Honoraria; AbbVie: Honoraria; Genentech: Honoraria; MEI Pharma: Honoraria. Griffiths: Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Takeda Oncology: Consultancy, Honoraria; Taiho Oncology: Consultancy, Honoraria; Apellis Pharmaceuticals: Research Funding; Novartis: Honoraria; Alexion Pharmaceuticals: Consultancy, Research Funding; Boston Biomedical: Consultancy; Astex Pharmaceuticals: Honoraria, Research Funding; Genentech: Research Funding; Abbvie: Consultancy, Honoraria. Lai: Astellas: Speakers Bureau; Jazz Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Speakers Bureau; Macrogenics: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees. Foran: trillium: Research Funding; actinium: Research Funding; kura: Research Funding; boehringer ingelheim: Research Funding; takeda: Research Funding; abbvie: Research Funding; aptose: Research Funding; pfizer: Honoraria; novartis: Honoraria; servier: Honoraria; bms: Honoraria; revolution medicine: Honoraria; OncLive: Honoraria; gamida: Honoraria; certara: Honoraria; sanofi aventis: Honoraria; syros: Honoraria; taiho: Honoraria; h3bioscience: Research Funding; aprea: Research Funding; sellas: Research Funding; stemline: Research Funding. Badar: Pfizer Hematology-Oncology: Membership on an entity's Board of Directors or advisory committees. Desai: Astex: Research Funding; Janssen R&D: Research Funding; Kura Oncology: Consultancy; Takeda: Consultancy; Bristol Myers Squibb: Consultancy; Agios: Consultancy. Ades: ABBVIE: Honoraria; CELGENE/BMS: Honoraria; NOVARTIS: Honoraria; TAKEDA: Honoraria; JAZZ: Honoraria, Research Funding; CELGENE: Research Funding. Brunner: Novartis, Celgene, Takeda, AstraZeneca: Research Funding; Celgene, Forty Seven Inc, Jazz: Other: Advisory Board. Carraway: Celgene, a Bristol Myers Squibb company: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Other: Independent review committee; Stemline: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Other: Independent review committee; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astex: Other: Independent review committee; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Prebet: BMS: Research Funding; BMS, Curios, Daichi: Consultancy. Patnaik: Kura Oncology: Research Funding; Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees; Stemline Therapeutics: Membership on an entity's Board of Directors or advisory committees. Savona: Karyopharm: Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Geron: Consultancy, Membership on an entity's Board of Directors or advisory committees; CTI: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS-Celgene: 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; Ryvu: Consultancy, 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; Taiho: Consultancy, Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; ALX Oncology: Research Funding; Astex: Research Funding; Incyte: Research Funding. Al-Kali: Novartis: Research Funding; Astex: Other: Research support to institution.

Background: Heterozygous somatic mutations in the genes encoding RNA splicing factors SF3B1, U2AF1, SRSF2 or ZRSR2 induce aberrant splicing in cancer cells and are among the most common mutations in patients with MDS, AML or CMML. H3B-8800 is an orally available small molecule that binds to the SF3b complex and induces alternative splicing changes in cells. Because splicing factor mutant cells depend on residual wild-type function of splicing factors for survival, we hypothesized that H3B-8800 would induce preferential cell killing of mutant cells by further perturbing splicing to synthetic lethality. In pre-clinical models, H3B-8800 preferentially kills spliceosome mutant cells and induces antitumor activity in xenograft leukemia models with core spliceosome mutations (Seiler M et al Nature Medicine 2018). Therefore, we conducted a phase I clinical trial (NCT02841540) of H3B-8800 in patients with MDS, AML or CMML. Here we describe the safety profile and clinical outcomes of the dose escalation cohorts in this phase I trial. Methods: This phase I trial explored the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of H3B-8800 in patients with myeloid cancers. Dose escalation cohorts, employing a standard 3+3 design, examined 2 different once daily dosing regimens (schedule I: 5 days on/9 days off; schedule II: 21 days on/7 days off) in a 28-day cycle, with stratification based on lower-risk (LR) versus higher-risk (HR) myeloid neoplasms. Results: As of June 16th, 2019, 84 patients were enrolled at 24 centers in the US and Europe. Dose ranged from 1-40 mg among 65 patients on schedule I, while 19 patients were enrolled with dose ranging from 7-20 mg on schedule II. The patient population included AML (n=38), CMML (n=4), HR-MDS (n=20), LR-MDS (n=21) and 1 MDS with unknown risk level. Most patients (88%) had spliceosome mutations of interest. The most common mutations were in SRSF2 (p.P95H in 17, p.P95L in 9, p.P95_R102Del in 4), SF3B1 (p.K700E in 11, p.R625C in 4), and U2AF1 (p.Q157P in 6, p.S34F in 4). Patients remained on treatment from 7 to 819 days; 25 patients (30%) had time on treatment greater than 180 days, 20% more than 1 year and 2% over 2 years. The median therapy duration for LR-CMML/MDS, HR-CMML/MDS, and AML patients were 216, 62, and 47 days respectively. Most observed treatment related treatment-emergent adverse events (TEAEs) were Grade 1 or 2. The most common treatment-related (as judged by the investigator, >10% frequency) TEAEs in the patients treated on schedule I were diarrhea (75%), nausea (37%), fatigue (28%) and vomiting (27%). The most common treatment-related TEAEs in the patients treated on schedule II were diarrhea (68%), vomiting (42%), QTc prolongation (21%), nausea (16%), and fatigue (16%). The most common dose limiting toxicity was prolongation of the QTcF interval >500 msec (n=2, 40 mg on schedule I and n=1, 20 mg on schedule II, all ≥Grade 3) and bradycardia without other arrhythmias (n=1, 14 mg on schedule II, ≥Grade 3). No ophthalmic AEs were observed; 1 patient (LR-MDS) experienced durable marrow aplasia. The maximum tolerated dose (MTD) has not been confirmed for either Schedule I or Schedule II. PK analysis indicates that H3B-8800 is rapidly absorbed and exhibits dose-proportional increase in plasma exposure. Consistent dose-dependent target engagement (i.e., alteration in mature mRNA transcripts) was observed in blood mononuclear cells from patients enrolled in the 2 mg up to 40 mg dose cohorts on both schedules. Despite this splicing modulation, no objective complete responses (CR) or partial responses (PR) meeting International Working Group criteria were observed. One patient with CMML had a durable platelet response that began in Cycle 1 and persisted through Cycle 13. Nine red blood cell (RBC) transfusion-dependent patients with MDS or CMML and 2 patients with AML did not require RBC transfusions for ≥8 weeks (up to 28 weeks) while on study. One platelet transfusion-dependent patient with LR-MDS did not require platelet transfusions for ≥8 weeks. Conclusion: Results from this first-in-human multicenter prospective clinical trial of a splicing modulator in myeloid neoplasms demonstrate dose-dependent target engagement and predictable PK profile of H3B-8800, and safety even with prolonged dosing. Although no objective CR or PR were achieved, decreased RBC or platelet transfusion requirements were observed in 12 (14%) of enrolled patients. Disclosures Steensma: H3 Biosciences: Other: Research funding to institution, not investigator.; Pfizer: Consultancy; Aprea: Research Funding; Stemline: Consultancy; Arrowhead: Equity Ownership; Summer Road: Consultancy; Astex: Consultancy; Onconova: Consultancy. Wermke:Novartis: Honoraria, Research Funding. Greenberg:Notable Labs: Research Funding; Celgene: Research Funding; Genentech: Research Funding; H3 Biotech: Research Funding; Aprea: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees. Font:Celgene: Consultancy, 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; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Komrokji:Agios: Consultancy; JAZZ: Speakers Bureau; DSI: Consultancy; JAZZ: Consultancy; Incyte: Consultancy; Novartis: Speakers Bureau; celgene: Consultancy; pfizer: Consultancy. Yang:Agios: Consultancy; AstraZeneca: Research Funding. Brunner:Astra Zeneca: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Forty Seven Inc: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Novartis: Research Funding. Ades:Agios: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Silence Therapeutics: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Helsinn Healthcare: Membership on an entity's Board of Directors or advisory committees. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding. Coombs:H3 Biomedicine: Research Funding. Foran:Agios: Honoraria, Research Funding. Garcia-Manero:Helsinn: Research Funding; Novartis: Research Funding; AbbVie: Research Funding; Celgene: Consultancy, Research Funding; Amphivena: Consultancy, Research Funding; Astex: Consultancy, Research Funding; Onconova: Research Funding; H3 Biomedicine: Research Funding; Merck: Research Funding. Micol:AbbVie: Consultancy; Jazz Pharmaceuticals: Consultancy. Perez De Oteyza:Celgene: Speakers Bureau. Wang:Abbvie: Other: Advisory role; Kite: Other: Advisory role; Jazz: Other: Advisory role; Astellas: Other: Advisory role, Speakers Bureau; celyad: Other: Advisory role; Pfizer: Other: Advisory role, Speakers Bureau; Stemline: Other: Advisory role, Speakers Bureau; Daiichi: Other: Advisory role; Amgen: Other: Advisory role; Agios: Other: Advisory role. Watts:Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees. Buonamici:H3 Biomedicine: Employment. Kim:H3 Biomedicine: Employment. Gourineni:H3 Biomedicine: Employment. Marino:H3 Biomedicine: Employment. Rioux:H3 Biomedicine: Employment. Schindler:H3 Biomedicine: Employment. Smith:H3 Biomedicine: Employment. Yao:H3 Biomedicine: Employment. Yuan:Eisai: Employment. Yu:H3 Biomedicine: Employment. Platzbecker:Abbvie: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding. OffLabel Disclosure: H3B-8800 (experimental, unapproved)

Abstract Introduction Population level data about the survival outcomes of patients with hematologic malignancies occurring as second cancers is limited. We undertook one of the largest analyses of second hematologic malignancies (SHM) using the Surveillance, Epidemiology & End Results (SEER) registry to identify factors associated with survival. Methods SEER 9 &13 registries were queried to identify adult patients (pts>18 years) diagnosed with SHM that comprised of Acute Myeloid Leukemia (AML), Acute Lymphoid Leukemia (ALL), Myelodysplastic Syndromes (MDS), Chronic Myeloid Leukemia (CML) & Other Acute Leukemias (OAL, biphenotypic leukemias, myeloid sarcomas & leukemias NOS) > 1 year (yr) after diagnosis of a primary unrelated cancer, using ICD-O-3 codes over a 40 yr period (1973-2012). Data on demographics, follow up, primary tumor & survival were abstracted. Univariate & multivariate analyses were performed to identify factors influencing survival of SHM & compared with hematologic malignancies occurring as first cancers. Hazard ratios (HR) with 95% confidence intervals (CIs) are reported & significance was set at p< 0.01. Results SHM cases included 4665 AML, 3569 MDS, 1140 OAL, 1076 CML & 536 ALL pts. Median age at diagnosis of SHM was 73 yrs (range, 18-100) for AML, 79 yrs (18-100) for MDS, 74 yrs(20-99) for OAL, 74 yrs(18-98) for CML & 70 yrs(19-97) for ALL. Pts>60 yrs comprised 79.2% of AML, 92% of MDS, 88.7% of OAL, 82.9% of CML & 75.2% of ALL cases. Gender distribution was similar across all categories, with females comprising 48.5% of AML, 42.2% of MDS, 45.3% of OAL, 42.8% of CML & 50.2% of ALL cases. More than 85% of pts in each group were Caucasians. While the majority of pts had one primary unrelated cancer (82-89%), 14% of AML pts, 17.8% of MDS pts, 13.8% of OAL, 15.3% of CML pts& 10.6% of ALL pts had >1 primary unrelated cancer. Most common primary sites were prostate (19.1-29.6%), breast (16.1-21.9%) & colorectal (9.3-14.5%). Median survival (range) was as follows: AML 0.2 yrs (0-28.2); MDS 1.5 yrs (0-14); OAL 0.2 yrs (0-29.1); CML 2.5 yrs (0-27.1); & ALL 0.7 yrs (0-28.8). Median latency periods (range) for secondary cancers were as follows: AML 5.2 yrs (1.0-24.2); MDS 7.6 yrs (1.0-35.5); OAL 5.7 yrs (1.0-=34.3); CML 5.2 yrs (1.0-31.6); & ALL 6.2 yrs (1.0-35.5). In univariable analyses, age <60 yrs predicted for better survival (p<0.0001) for all SHM, as did diagnosis in recent yrs (2001-2012) (p< 0.0001 for AML, OAL, CML & ALL). Effect of time period on survival for MDS was not done, as it became formally reportable in 2001. Having >2 primaries was associated with an unfavorable outcome for subsequent AML (HR=1.15; 1.08-1.23; p < 0.0001), MDS (HR=1.13; 1.05-1.22: p=0.001) & CML (HR=1.30; 1.13-1.48: p=0.0002). In multivariable analyses, advancing age was an independent adverse prognostic factor for all secondary leukemias & MDS, both as a continuous variable & when categorized as <60 yrs vs. >60 yrs (p<0.001). Race & gender did not impact survival. Using breast cancer as a referent primary, AML pts had worse outcomes following colorectal (HR=1.31; 1.14-1.5; p=0.0002) or lung (HR=1.46; 1.22-1.74; p< 0.0001) primaries, while MDS pts fared worse with prior lung (HR=1.61; 1.22-2.12; p=0.0007) or Non-Hodgkin lymphoma (HR=1.58; 1.3-1.92: p< 0.0001). Of all 2ndCML cases, those after colorectal cancer had worst survival (HR=1.54; 1.12-2.13; p=0.008). Among SHM pts, MDS pts had better survival than those with AML (HR=0.42; 0.4-0.44: p< 0.0001), as did pts with CML (HR=0.37; 0.35-0.41: p< 0.0001) & ALL (HR=0.64; 0.58-0.70; p< 0.0001). Out OAL had similar outcomes compared to AML (HR=0.99; 0.92-1.05; p=0.66). Pts with CML fared better than MDS (HR=0.47; 0.41-0.54; p< 0.0001) & OAL (HR=0.37; 0.34-0.41: p< 0.0001). Pts with ALL had worse survival than CML (HR=1.8; 1.6-2.03: p< 0.0001) & MDS (HR=1.28; 1.11-1.48: p=0.0005), but better than OAL (HR=0.65; 0.58-0.73: p< 0.0001). (Figure 1) Patients with all SHM, except CML, had worse outcomes compared to those with primary hematologic cancers (Figure 2). Conclusion The prolonged latencies for SHM in this study suggest that they are likely therapy-related. Our findings show that type & number of primary cancers influence survival of subsequent leukemias & MDS. SHM have worse survival compared to those with primary hematologic malignancies except CML where non-separation of survival curves suggest that CML as SHM does not behave like a therapy-related neoplasm. Disclosures Sekeres: TetraLogic: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees.

Abstract Background: SL-401 is a novel targeted therapy directed to the interleukin-3 receptor (CD123), a target overexpressed by many hematologic malignancies. SL-401 is currently being advanced through clinical trials in patients with a variety of CD123+ malignancies including blastic plasmacytoid dendritic cell neoplasm (BPDCN), acute myeloid leukemia (AML) in remission with high relapse risk, and multiple myeloma. CD123 has been shown to be expressed on myeloproliferative neoplasm (MPN) cells as well as microenvironmental immune cells, namely plasmacytoid dendritic cells (pDCs), in the bone marrows of some patients with MPN including chronic myelomonocytic leukemia (CMML). Microenvironmental pDCs have been implicated in promoting plasma cell disorders and preliminary data suggest that pDCs could play a related role in some myeloid neoplasms. Accordingly, a therapy directed at both CD123-expressing myeloid cells and neighboring CD123-expressing pDCs could provide therapeutic benefit. SL-401 is being evaluated in patients with advanced, high-risk MPN, including systemic mastocytosis (SM), myelofibrosis (MF), primary eosinophilic disorders (PED), and CMML. Preliminary results are reported here. Methods & Results: This multicenter, single-arm Phase 2 trial of patients with advanced, high risk MPN includes a lead-in (stage 1) and expansion (stage 2). In stage 1, patients receive SL-401 as a daily IV infusion at 7, 9, 12 ug/kg/day, or higher for days 1-3 of a 21-28 day cycle in a 3x3 design. In stage 2, patients receive SL-401 at the dose determined in stage 1. Study objectives include characterization of the safety profile, including determination of the maximum tolerated or tested dose, and detection of preliminary efficacy signals including evaluation of tumor response and progression free survival by standard criteria. As of 7/20/16, 6 patients with MPN (MF, n=3; CMML-2, n=2; CMML-1, n=1) received SL-401 (7 ug/kg, n=3; 9 ug/kg, n=3). The median age was 66 years (range: 42-81 years). Patients treated at all doses received 1+ to 2+ cycles (ongoing) of SL-401. The most common treatment-related adverse events (AEs) were thrombocytopenia (2/6; 33%) and fatigue (2/6; 33%); the most common ≥ Grade 3 treatment-related AEs were thrombocytopenia (2/6; 33%) and anemia (1/6; 17%); there has been no DLT. Efficacy assessments are ongoing. Patients are currently enrolling in the 12 ug/kg/day cohort. Conclusions: Initial dosing of SL-401 appears to be well-tolerated in patients with MPN and CMML, with no unexpected AEs observed. Given CD123 expression on myeloid neoplastic cells as well as microenvironmental immune cells (namely, pDCs), SL-401 may offer a novel, targeted therapeutic approach in patients with high-risk MPN and CMML of unmet medical need. Enrollment continues in stage 1 of this ongoing Phase 2 trial and updated safety and efficacy data will be presented. Clinical trial information: NCT02268253. Disclosures Gupta: Novartis: Consultancy, Honoraria, Research Funding; Incyte Corporation: Consultancy, Research Funding. Carraway:Incyte: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Baxalta: Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees. Schiller:Incyte Corporation: Research Funding. Talpaz:Incyte Corporation: Other: Travel expense reimbursement, Research Funding; Ariad: Other: Expense reimbursement, travel accomodation expenses, Research Funding; Novartis: Research Funding; Pfizer: Consultancy, Other: travel accomodation expenses, Research Funding. McCloskey:Novartis: Speakers Bureau; Incyte: Consultancy; Ariad: Consultancy, Speakers Bureau; Amgen: Speakers Bureau. Lee:Alexion Pharmaceuticals: Consultancy; Amgen: Consultancy; Baxalta: Consultancy; Boehringer Ingelheim: Consultancy; Pfizer Inc: Consultancy. Yacoub:Alexion: Honoraria; Seattle Genetics: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau. Ali:Incyte Corporation: Research Funding. Chen:Stemline Therapeutics, Inc.: Employment, Equity Ownership. Shemesh:Stemline Therapeutics: Employment, Equity Ownership. Brooks:Stemline Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties.

Abstract Background: The incidence of thyroid cancers has been rising in the United States primarily due to the increased detection of well differentiated thyroid cancers (WDTC). Radioactive iodine (RAI), which is frequently used to treat WDTC, can be considered a circulating radiation emitter with the potential for mutagenic effects on hematopoietic stem cells. With a growing number of WDTC patients (pts) surviving long term following RAI therapy, establishing the risk of developing a myelodysplastic syndrome (MDS) in this cohort has important clinical implications. Methods: A novel R program, SEERaBomb (Radiat Environ Biophys. 2014;53(1):55-63) was used to query all 18 Surveillance Epidemiology and End Results (SEER) registries to identify WDTC cases treated with RAI and MDS as second cancers. SEERaBomb allows merging of all 18 SEER registries - a function not permitted by the SEER*Stat MP-SIR that limits researchers to use to one of two datasets (SEER 9 or SEER 13), thereby significantly increasing the capture of MDS cases (Figure 1). WDTC includes papillary and follicular thyroid histologies. WDTC survivor person-years at risk for developing MDS was based on age at diagnosis of WDTC, survival time, and age at diagnosis of MDS. Relative risks (RR) for developing MDS were then based on observed/expected cases between the cohorts receiving surgery alone (control), surgery combined with RAI as well as those receiving external beam radiation therapy (EBRT) and surgery with or without (+/-) RAI. Mean radiation exposure to bone marrow was compared between RAI and prostate cancer (as example) treated with other radiation modalities - brachytherapy (seeds), EBRT (3D, IMRT and VMRT). Results: In total 132,157 WDTC patients were identified from 1973-2011, of whom 69,975 (53%) received surgery alone, 59,015 (45%) underwent surgery + RAI and 3167 (2%) underwent EBRT [combined with surgery+/- adjuvant RAI]. Mean age at the time of WDTC diagnosis was: 49.4 years (yrs, range, 2-105) in the surgery group; 46.7 yrs (2-99) in the surgery + RAI group and 55.1 yrs (10-101) in the EBRT group. Median person years of follow up after WDTC diagnosis was: 6.1 yrs (2.5-11.6) in pts undergoing thyroidectomy; 5.4 yrs (2.4-9.7) in the surgery + RAI group and 5.9 yrs (1.7-11) in the EBRT group. A total of 55 patients developed MDS; 24 had surgery alone, 27 received surgery + RAI and 4 had EBRT. Median time to development of MDS after WDTM diagnosis (25-75 interquartile range) was: 6.4 yrs (4-15) in pts receiving surgery alone; 4 yrs (1.7-6.7) in the surgery + RAI group and 3.6 yrs (2.4-7.9) in the EBRT group. MDS cases were classified as RA (n=11), RARS (n=2), RCMD (n=3), RAEB (n=9), MDS with 5q deletion syndrome (n=1), and MDS-U (n=29). Compared to patients definitively treated with surgery, those who additionally received RAI (+/- EBRT) had a statistically significantly increased risk of developing MDS within the first two years of exposure (RR=1.9; 95% CI, 0.43-5.61 vs. RR=5.8; 95% CI, 2.84-12.22). Beyond 2 years, the risk for MDS drops to baseline rates, and a trend observed beyond 12 years, which did not reach statistical significance (Figure 2). Conclusion: WDTC pts undergoing RAI treatment appear to have an increased risk of developing MDS within the first two years of exposure to RAI. It is difficult to determine whether this early excess risk is true risk or an effect of ascertainment bias (RAI pts followed more closely), as the kinetics of RAI indicate a lower magnitude of bone marrow exposure compared to other radiation modalities (Figure 3). Considering the long latency of MDS seen in atomic bomb cohorts, relative young age of WDTC pts, current trend towards overdiagnosis and overtreatment of WDTCÕs, MDS rates are likely to continue to rise. Disclosures Sekeres: Celgene Corporation: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; TetraLogic: Membership on an entity's Board of Directors or advisory committees.

Abstract Among mechanisms underlying cytotoxic drug resistance is activation of diverse DNA damage response (DDR) pathways. Poly(ADP-ribose) polymerases (PARP)-1/2 facilitate both single- and double-strand break (DSB) repair and play a key role in the base excision repair (BER) of chemotherapy-damaged DNA. The PARP inhibitor veliparib (V) potentiates the cytotoxicity of different chemotherapeutics, including temozolomide (TEM). TEM induces distinct alkylating events in neoplastic cells whose ultimate outcome depends on the interaction of BER, mismatch repair (MMR), O(6)-methylguanine-DNA methyltransferase (MGMT), and DSB repair. While clinical activity of TEM has been mainly observed in MGMT-deficient AML, V potentiated cytotoxicity of TEM in leukemia cells in vitro in the setting of MGMT overexpression or deficient MMR pathway (Mol Cancer Ther, 2009). Methods: We conducted a Phase I study to determine maximum tolerated dose (MTD) and recommended Phase II dose (RP2D) of V+TEM, using a 3+3 dose escalation. Patients (pts) ≥60 years (yrs) with newly diagnosed poor cytogenetic-risk AML/ALL who were not candidates for intensive therapy, or ≥18 yrs with relapsed/refractory AML/ALL, secondary AML (therapy-related or arising from MDS or MPN), and CMMoL-2 were eligible. Any number of prior regimens, including allogeneic transplant (alloSCT), were allowed. V was given orally day (d)1 once, then twice a day on d4-12 at one of 6 dose levels (DL) (DL1A-B 20mg; DL2-DL3-DL4-DL5-DL6: 40-80-120-150-200 mg). TEM was given orally once a day on d3-9 (DL1A 150 mg/m2/d; DL1B-DL6 200 mg/m2/d). 28-day cycles (cy) were repeated depending on response/tolerability (4-6 weeks delay allowed) with V on d1-8 and TEM d1-5. TEM was taken on empty stomach with antiemetics and V was taken irrespective of meals. Results: Forty-nine pts with median age 69 yrs (range, 22-88; 47% ≥70) were treated. Of 47 AML pts, 29 (62%) had secondary AML and 27 (57%) adverse karyotype. Median number of prior treatments for AML was 1 (range, 0-6): 18 (38%) had median 1 prior therapy (range, 1-3) for MDS; 30 (64%), 9 (18%), 34 (69%) received hypomethylating agents, alloSCT and intensive chemotherapy, respectively. Overall 42 (85%) pts were refractory to their last treatment. Pts received a median of 1 (range, 1-7) cy of therapy. Two did not complete cy 1, pt withdrawal d5 and progressive fungal pneumonia d9 with death d15 of progressive disease (PD). The MTD/RP2D was defined at V 150 mg and TEM 200 mg/m2; 2 of 4 pts treated at V 200 mg and TEM 200 mg/m2 developed dose-limiting toxicity of grade (gr) 3 oral mucositis/esophagitis. The most frequent drug-related toxicities (NCI CTC v4) were gr 1/2 nausea/vomiting (39%), fatigue (26%), oropharyngeal mucositis (26%), constipation (12%), and diarrhea (10%). Other common toxicities were infectious, including febrile neutropenia (29%), pneumonia (20%), bacteremia (18%). One (2%) pt died ≤d30 and 12 (24%) ≤d60 mainly of PD (1 pt fungal pneumonia before count recovery d31). Overall response rate was 33% (complete remission (CR), hematologic improvement (HI)/stable disease) with 8 (16%) pts achieving CR (1 CRi). Median overall survival was 5.03 months, for all responders 11.58 months, and for CR pts 19.89 months (Fig 1). Responses occurred at all DLs. Three CR pts underwent alloSCT; 2 remain in CR at ~3 yrs. Pharmacokinetics (PK): V or TEM PKs were not altered with co-administration. There was a correlation between the DLT of mucositis and V single (Cmax P=0.005; AUC P=0.009) and multiple dose exposure (Cmax P = 0.02; AUC P=0.03). Pharmacodynamics and pharmacoepigenetics: Four of 39 pts examined had MGMT methylation (3 CR; 75%) and 2 had BRCA-1 methylation (1 HI) in peripheral blood (PB) or bone marrow (BM) mononuclear cells (MC). Defective FancD2 pathway was observed in the BMMC of 19/19 pts using FancD2 ubiquitylation assays but did not correlate with response. V reduced PAR levels by >75% in PBMC of most pts and in the presence of TEM. Induction of γ-H2AX in CD34+ cells was seen upon V/V+TEM treatment. Conclusion: V plus TEM demonstrated safety and activity in this resistant and elderly leukemia population. Response rate was higher in MGMT methylated pts, but responses were also seen in pts who had no MGMT methylation, had failed multiple therapies, had secondary AML and/or adverse karyotype. Future clinical study should aim to identify pts with defective DDR pathways who are most likely to respond to this therapeutic approach. Figure 1. Figure 1. Disclosures Off Label Use: Temozolomide is not approved for AML. Beumer:Millenium: Other: Research support. Gore:Celgene: Consultancy, Honoraria, Research Funding.

Abstract Introduction: Surveillance, Epidemiology, and End Results (SEER) registry captures data on acute leukemias (AL) that morphologically do not conform to well characterized acute leukemic entities in the established French-American-British (FAB) nomenclature. Not much is known about population level outcomes of these rare AL. We performed a comprehensive survival analysis of these rare AL over a forty-year period using the SEER registry. Methods: SEER 18 dataset was queried to identify adult patients (pts > 18 years) diagnosed with Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL) and rare AL from 1973-2012. Rare AL cases were identified using ICD-O-3 morphology codes and included Leukemias, Not Otherwise Specified (NOS) (9800-01, 9860) and myeloid sarcoma (9930). Data on demographics,follow up and survival was abstracted. Univariate and multivariate analysis was performed to identify factors influencing survival of rare AL and survival patterns were compared to AML and ALL. Hazard ratios (HR) with 95% confidence intervals (CIs) are reported. Results: We identified 61,550 AML pts, 13,457 ALL pts, 525 myeloid sarcoma pts and 13,446 pts with leukemia NOS. Median age at diagnosis was 68 years (yrs, range 18-100) for AML, 54 yrs (18-100) for ALL, 65 yrs (18-95) for myeloid sarcoma and 76 yrs (18-100) for leukemia NOS. Gender distribution was similar with females comprising 45.9% of AML, 43% of ALL, 42.3% of myeloid sarcoma and 47.2% of leukemia NOS cases. Over 80% pts in all categories were Caucasian. Median survival was as follows: 0.4 (0-40) yrs for AML; 1.4 (0-39.8) yrs for ALL; 0.7 (0-32.9) yrs for Myeloid Sarcoma; and 0.3 (0-38.9) yrs for leukemia NOS. In univariable analysis, younger age predicted for better survival for both myeloid sarcoma and leukemia NOS (p<0.0001). Improvement in survival over time period was observed for pts with leukemia NOS (p < 0.0001). In multivariable analysis, advancing age was an independent prognostic factor for rare AL, both as a continuous variable and when categorized as older vs. younger pts using age cutoff of 60 yrs. Compared to younger pts, HR for pts > 60 yrs with rare AL was as follows: 2.68 (2.13-3.37; p <0.0001) for myeloid sarcoma; and 2.18 (2.07-2.31; p<0.0001) for leukemia NOS. No difference in survival over time was seen for myeloid sarcoma. Pts with leukemia, NOS diagnosed in yrs 2006-2012 (HR=0.87; 0.82-0.92; p < 0.0001) had better survival compared to the referent years 1973-80. Race and gender did not impact survival. In multivariable analysis, pts with leukemia NOS did worse overall compared to AML (HR=1.13; 1.11-1.53; p<0.0001) and ALL (HR=1.86; 1.81-1.91; p<0.0001). Interestingly, younger pts had a poorer outcome than AML (HR=1.10; 1.04-1.16; p=0.0003), but pts > 60 yrs had a better outcome (HR=0.93; 0.91-0.95; p<0.0001). Both younger (HR=1.33; 1.26-1.41; p<0.0001) and older pts (HR=1.45, 1.40-1.50: p<0.0001) compared unfavorably to ALL (Figure 1). Pts with myeloid sarcoma had a better survival compared to AML pts (HR=0.77; 0.7-0.85; p<0.0001) (Figure 2). This was uniform for pts <60 yrs (HR=0.77; 0.64-0.93; p=0.006) and > 60 yrs (HR= 0.77; 0.69-0.87; p<0.0001). Conclusion: Pts with leukemias NOS have poor outcomes compared to AML and ALL but prognosis has improved in recent years. The most probable explanation is identification of prognostic molecular mutations that has allowed accurate risk-stratification of pts using the WHO classification and in turn better selection of treatment strategies. Several reasons have limited our understanding of these rare AL - small numbers, exclusion from clinical trials and wide variability in treatment options used. Efforts at better molecular characterization of these AL holds the most promise for improving outcomes. Disclosures Sekeres: Celgene Corporation: Membership on an entity's Board of Directors or advisory committees; TetraLogic: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees.

Purpose To investigate the risk and outcomes of second hematologic malignancies (SHMs) in a population-based cohort of patients with well-differentiated thyroid cancer (WDTC) treated or not with radioactive iodine (RAI). Methods Patients with WDTC were identified from SEER registries. Competing risk regression analysis was performed to calculate the risks of SHMs that occurred after WDTC treatment and outcomes after SHM development were assessed. Results Of 148,215 patients with WDTC, 53% received surgery alone and 47% received RAI. In total, 783 patients developed an SHM after a median interval of 6.5 years (interquartile range, 3.3 to 11.2 years) from WDTC diagnosis. In multivariable analysis, compared with those undergoing thyroidectomy alone, RAI treatment was associated with an increased early risk of developing acute myeloid leukemia (AML; hazard ratio, 1.79; 95% CI, 1.13 to 2.82; P = .01) and chronic myeloid leukemia (CML; hazard ratio, 3.44; 95% CI, 1.87 to 6.36; P < .001). This increased risk of AML and CML after RAI treatment was seen even in low-risk and intermediate-risk WDTC tumors. Occurrence of AML but not CML in patients with WDTC was associated with shorter median overall survival compared with matched controls (8.0 years v 31.0 years; P = .001). In addition, AML developing after RAI trended toward inferior survival compared with matched controls with de novo AML (median overall survival, 1.2 years v 2.9 years; P = .06). Conclusion Patients with WDTC treated with RAI had an increased early risk of developing AML and CML but no other hematologic malignancies. AML that arises after RAI treatment has a poor prognosis. RAI use in patients with WDTC should be limited to patients with high-risk disease features, and patients with WDTC treated with adjuvant RAI should be monitored for myeloid malignancies as part of cancer surveillance.

Abstract Purpose: The PARP inhibitor veliparib delays DNA repair and potentiates cytotoxicity of multiple classes of chemotherapy drugs, including topoisomerase I inhibitors and platinating agents. This study evaluated veliparib incorporation into leukemia induction therapy using a previously described topotecan/carboplatin backbone. Experimental Design: Employing a 3+3 trial design, we administered escalating doses of veliparib combined with topotecan + carboplatin in relapsed or refractory acute leukemias, aggressive myeloproliferative neoplasms (MPN), and chronic myelomonocytic leukemia (CMML). Results: A total of 99 patients received veliparib 10–100 mg orally twice daily on days 1–8, 1–14, or 1–21 along with continuous infusion topotecan 1.0–1.2 mg/m2/d + carboplatin 120–150 mg/m2/d on days 3–7. The MTD was veliparib 80 mg twice daily for up to 21 days with topotecan 1.2 mg/m2/d + carboplatin 150 mg/m2/d. Mucositis was dose limiting and correlated with high veliparib concentrations. The response rate was 33% overall (33/99: 14 CR, 11 CRi, 8 PR) but was 64% (14/22) for patients with antecedent or associated aggressive MPNs or CMML. Leukemias with baseline DNA repair defects, as evidenced by impaired DNA damage–induced FANCD2 monoubiquitination, had improved survival [HR = 0.56 (95% confidence interval, 0.27–0.92)]. A single 80-mg dose of veliparib, as well as veliparib in combination with topotecan + carboplatin, induced DNA damage as manifested by histone H2AX phosphorylation in CD34+ leukemia cells, with greater phosphorylation in cells from responders. Conclusions: The veliparib/topotecan/carboplatin combination warrants further investigation, particularly in patients with aggressive MPNs, CMML, and MPN- or CMML-related acute leukemias. Clin Cancer Res; 23(4); 899–907. ©2016 AACR.