Citations

e24108 Background: Clonal hematopoiesis of Indeterminate Potential (CHIP) is associated with adverse clinical outcomes including increased risk of hematologic malignancies and heart disease. Limited data suggest an increased prevalence of CHIP in patients treated for solid tumors, particularly after exposure to radiation and chemotherapy. CHIP testing may inform risk-reduction strategies for cancer survivors. Little is known about patient knowledge, attitudes, and preferences regarding CHIP testing. Methods: We surveyed survivors without history of recurrence participating in an ongoing prospective cohort study of young women with breast cancer (BC). The survey was sent by email and included an introduction to CHIP including risk factors and clinical associations. Respondents then reviewed a vignette and were asked about CHIP testing preferences (definitely/probably test vs. definitely/probably not test) considering sequentially: 1) population-based 10-year risk of BC recurrence, hematological malignancy and heart disease; 2) estimated increase in these risks with CHIP; 3) current CHIP management; 4) a dedicated CHIP clinic; and 5) a theoretical CHIP treatment. Changes in preferences from the prior scenario were evaluated with the McNemar's test using a type I error rate of 5%. Results: 528/642 (82.2%) eligible women responded to the survey, at a median age of 46 (range: 31-54) years (median time from diagnosis: 108 months (range: 60-168)), and 88% were white. Most had stage 1/2 BC (78.8%) and had received chemotherapy (73.1%) and/or radiation (61.9%). 93.6% had never heard of CHIP prior to survey. After initial patient vignette presentation, most women (87.1%,) recommended CHIP testing if offered. Preferences for testing decreased (p<0.05) when considering population-based risks, with 11.1% shifting their preference from CHIP testing to not testing. After considering increased risks associated with CHIP, interest in testing increased (p<0.05), with 10.1% shifting their preference to testing. Interest significantly (p<0.05) increased with the possibility of managing CHIP through a clinic or a hypothetical CHIP treatment, with 7.2% and 14.1% switching their preferences towards testing, respectively. Finally, 75.8% responded that they themselves, after learning about CHIP and reviewing the vignette, would want to have CHIP testing; 28.2% reported that learning about CHIP and the associated risks caused them at least moderate anxiety. Conclusion: Few young BC survivors were aware of CHIP yet most indicated an interest in testing after learning about it. Testing preferences were influenced by risks presented and potential management strategies. Findings highlight the importance of effective risk communication and the need for adequate psychosocial support when considering testing for CHIP and other potential clinical biomarkers predictive of cancer and other medical risks in cancer survivors.

TPS3161 Background: The p53 pathway has been implicated in antitumor immunity, including antigen presentation and T-cell proliferation. Loss of p53 function can increase resistance to immunotherapy across many tumor types. Eprenetapopt (eprenet) is a small molecule that stabilizes the folded structure of p53, resulting in activation of mutant p53 and stabilization of wild-type (WT) p53. It also targets the cellular redox homeostasis, resulting in induction of apoptosis in tumor cells. In vivo, mice carrying supernumerary copies of the TP53 gene harbor a pro-inflammatory tumor microenvironment, an effect recapitulated in TP53 normal-copy mice treated with eprenetapopt. Combining eprenetapopt and anti-PD1 or anti-CTLA4 therapy resulted in enhanced tumor growth inhibition and improved survival in TP53 WT mice inoculated with B16 melanoma and MC38 colon adenocarcinoma cells . Based on these results, we hypothesized that eprenet-induced p53 stabilization may augment response to immunotherapy. To test this hypothesis, we are conducting a phase 1b/2 study of eprenet in combination with pembrolizumab (eprenet+pembro) in pts with solid tumors. Methods: The primary objectives are to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) and to assess the safety and tolerability of eprenet+pembro in pts with advanced solid tumors. The secondary objectives are to estimate the anti-tumor activity and to describe the pharmacokinetics of the combination. Exploratory objectives include assessing predictive and pharmacodynamic markers of response. The study includes a safety lead-in with a 3+3 dose de-escalation design for pts with advanced solid tumors with known tumor TP53 mutation status ( TP53 WT is acceptable) (max 18 pts), followed by expansion cohorts in pts with NSCLC, gastric/GEJ and urothelial cancer (max 100 pts). In expansion, pts with urothelial and gastric cancers must be naïve to anti-PD-1/ L1 therapy. Eprenet is given IV once daily on Days 1–4 while pembro is administered on Day 3 of each 21-day cycle. The RP2D of eprenet+pembro is considered the dose at which ≤ 1 of 6 pts in a cohort has a dose-limiting toxicity (DLT). Primary endpoints are occurrence of DLTs, adverse events (AEs) and serious AEs with eprenet+pembro. Key secondary endpoints are best objective response, progression free survival and overall survival. Exploratory endpoints include gene mutations by next generation sequencing (including TP53), mRNA expression, multiplex immunohistochemistry and transcriptomics, multiplex flow cytometry on peripheral blood mononuclear cells and cytokines in serum. Continuous monitoring of toxicity will be conducted. The trial opened in May 2020 and is actively enrolling patients. Clinical trial information: NCT04383938.

2014 Background: The cyclin D-CDK4/6-Rb pathway is activated in most glioblastomas. Abemaciclib is a potent CDK4/6 inhibitor with good brain penetration approved for HR+/HER2- breast cancer. In order to efficiently evaluate the potential impact of abemaciclib on overall survival (OS) in newly diagnosed glioblastoma and to simultaneously develop information regarding potential genomic biomarker associations, abemaciclib was included as an arm on the Individualized Screening Trial of Innovative Glioblastoma Therapy (INSIGhT) trial. INSIGhT is a phase II platform trial using response adaptive randomization and deep genomic profiling to more efficiently test experimental agents in MGMT unmethylated glioblastoma and potentially accelerate identification of novel therapies for phase III testing. Initial randomization was equal between abemaciclib, control, and two other experimental arms but subsequent randomization was adapted based on efficacy as determined by progression-free survival (PFS). Ineffective arms were discontinued and new arms added by protocol amendment. We report preliminary results for the abemaciclib arm which has completed accrual. Methods: Patients with newly diagnosed MGMT-unmethylated glioblastoma were randomized to receive either radiotherapy with concomitant and adjuvant temozolomide at standard doses or standard radiochemotherapy followed by adjuvant abemaciclib (150-200 mg orally BID). Treatment continued until progression or development of unacceptable toxicities. The primary endpoint was OS which was assessed using the log-rank test estimated via the Kaplan Meier method using a type I error of 5%. The hazard ratio (HR) was estimated using a cox proportional hazards model. Association between abemaciclib efficacy and cyclin D-CDK4/6-Rb pathway genomic alterations was also investigated. Results: There were 142 patients (69 control; 73 treated with abemaciclib). Abemaciclib was generally well-tolerated with no new toxicity signals identified. PFS was significantly longer (HR 0.67; p = 0.03, logrank test) with abemaciclib (median 6.54 months) compared to the control arm (median 5.88 months). For patients with activation of the CDK4 pathway the PFS HR was 0.64 (p-value = 0.04). However, there was no significant improvement in overall survival (HR 0.9; p-value > 0.05) between abemaciclib (median 15.5) compared to the control arm (median 15.5). Conclusions: Abemaciclib was well-tolerated and prolonged PFS but there is no evidence of an overall survival improvement compared to standard radiochemotherapy. Clinical trial information: NCT02977780.

2006 Background: Adaptive randomization adjusts enrollment rates based upon early trial results, which can allow for decreased enrollment for therapies less likely to meet the primary endpoint of a trial. CC-115, a CNS-penetrant, oral inhibitor of mammalian target of rapamycin kinase (mTOR) and deoxyribonucleic acid-dependent protein kinase (DNA-PK), was evaluated in the Individualized Screening Trial of Innovative Glioblastoma Therapy (INSIGhT) trial. As CC-115 was discontinued due to concerns about toxicity and unfavorable risk-to-benefit ratio, we sought to investigate the impact of adaptive randomization in its testing. Methods: In INSIGhT, adults with newly diagnosed MGMT-unmethylated glioblastoma and available genomic data are adaptively randomized to an experimental arm or the control arm of standard radiotherapy with concurrent and adjuvant temozolomide. Patients randomized to CC-115 received it (10mg po BID) with radiotherapy and as adjuvant monotherapy, and a safety lead-in 3+3 design was used for this arm. By simulating the INSIGhT trial with standard uniform randomization, we estimated the reduction of enrollment rate and sample size of the CC-115 arm that was attributable to adaptive randomization. Results: Twelve patients were randomized to CC-115; 58% (n = 7) patients had possible treatment-related CTCAE grade > 3 toxicity. Compared to the control arm, there was no significant difference in progression-free survival (PFS, HR 0.66, 95% CI 0.32-1.36, p = 0.3) or overall survival (OS, HR 0.93, 95% CI 0.43-2.03, p = 0.8). Based on early PFS results, randomization probability to CC-115 decreased from 25% to 16%. At the time of the CC-115 arm closure, 14% of enrolled INSIGhT patients had been randomized to this arm. Compared to average expected enrollment by standard randomization, the use of adaptive randomization decreased the number of patients randomized to CC-115 by 50% (12 patients vs. 18 patients [95% CI 11-25 patients]). Conclusions: The INSIGhT trial, designed with adaptive randomization, facilitated more efficient testing of CC-115 and decreased the number of patients allocated to the CC-115 arm relative to a standard randomization design. Clinical trial information: NCT02977780.

Abstract BACKGROUND: Recurrent isocitrate dehydrogenase (IDH) 1 mutations are observed in 6-10% of patients with acute myeloid leukemia (AML). Ivosidenib (AG-120), a potent, selective, oral, small-molecule inhibitor of the mutant IDH1 (mIDH1) protein, is a promising therapeutic candidate for the treatment of patients with mIDH1 AML. Through inhibition of mIDH1, ivosidenib suppresses the abnormal production of the oncometabolite 2-hydroxyglutarate (2-HG), leading to clinical responses via differentiation of malignant cells. AIM: To report safety and efficacy data from the first-in-human phase 1 study of ivosidenib in patients with mIDH1 advanced hematologic malignancies including relapsed/refractory (R/R) AML (NCT02074839). This is the first report of data from the 4 expansion cohorts, with a total of 258 patients treated on study. METHODS: The ongoing phase 1 study assesses the safety, maximum tolerated dose (MTD), pharmacokinetics, pharmacodynamics, and clinical activity of ivosidenib in mIDH1 hematologic malignancies. Enrollment was completed on May 8, 2017. During dose escalation, patients received ivosidenib as a single agent orally once daily (QD) or twice daily (BID) in 28-day cycles. The MTD was not reached and 500 mg QD was selected as the recommended dose to be tested in 4 expansion cohorts: R/R AML (Arms 1 and 4, where Arm 1 patients are those with relapse after transplantation, second or later relapse, resistance to initial induction or reinduction treatment, or relapse within 1 year of initial treatment, and Arm 4 patients have R/R AML but are not eligible for Arm 1); untreated AML (Arm 2); and other advanced hematologic malignancies including myelodysplastic syndrome (MDS) (Arm 3). Updated safety data will be presented for all patients. Efficacy outcomes will be presented for all R/R AML patients treated at 500 mg QD across the dose escalation and expansion cohorts who received their first dose of ivosidenib at least 6 months prior to the analysis cut-off date of May 12, 2017, as well as for the poorest prognosis Arm 1 subset. Efficacy data for all treated patients from the other expansion cohorts (untreated AML and other advanced hematologic malignancies including MDS) will also be presented. RESULTS: In all, 258 patients (78 in dose escalation, 180 in expansion) were treated with ivosidenib. As of May 12, 2017, 62 of 258 (24%) patients were continuing on treatment. The median duration of exposure to ivosidenib was 3.5 months (range 0.1-33.5). Twenty-two (8.5%) patients discontinued treatment to proceed to allogeneic stem cell transplantation. Treatment was well tolerated; the most common adverse events (AEs) (n=258) of any grade irrespective of causality occurring in ≥20% of patients were diarrhea (33%), leukocytosis (30%), nausea (30%), fatigue (29%), febrile neutropenia (25%), dyspnea (24%), anemia (23%), QT prolongation (23%), peripheral edema (22%), pyrexia (21%), and decreased appetite (20%). The majority of these AEs were grades 1-2 and reported as unrelated to treatment. Differentiation syndrome (DS) was observed in 29 of 258 (11.2%) patients, including grade ≥3 DS in 14 (5.4%); study drug was held owing to DS in 11 patients (4.3%), and no instances of DS led to permanent treatment discontinuation or death. The primary efficacy endpoint for R/R AML is the CR+CRh rate, i.e., the rate of complete remission (CR according to modified IWG 2003 criteria plus CR with partial hematologic recovery, defined as CR except absolute neutrophil count &gt;0.5 × 109/L [500/µL] and platelet count &gt;50 × 109/L [50,000/µL]). Among 125 Arm 1 R/R AML patients receiving ivosidenib 500 mg QD across dose escalation and expansion who received their first dose at least 6 months prior to the analysis cutoff date, the CR+CRh rate was 30.4% (95% CI 22.5%, 39.3%), including CR in 27 (21.6%) and CRh in 11 (8.8%) patients. Median duration of CR+CRh was 8.2 months (95% CI 5.5, 12.0), and duration of CR was 9.3 months (95% CI 5.6, 18.3). The overall response rate (CR+CRi/CRp+PR+MLFS) was 41.6% (95% CI 32.9%, 50.8%) (52/125 patients). CONCLUSION: Ivosidenib monotherapy is well tolerated in patients with mIDH1 AML and other advanced hematologic malignancies. In a high-risk, molecularly defined R/R AML patient population with unmet medical need, ivosidenib induced durable remissions and improved patient outcomes. These findings support the role of ivosidenib as an effective, oral, targeted treatment for patients with mIDH1 AML. Disclosures DiNardo: Celgene: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Agios: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. De Botton: Pfizer: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Servier: Honoraria; Agios: Honoraria, Research Funding. Stein: GSK: Other: Advisory Board, Research Funding; Constellation Pharma: Research Funding; Seattle Genetics: Research Funding; Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Celgene Corporation: Consultancy, Other: Travel expenses, Research Funding; Pfizer: Consultancy, Other: Travel expenses; Novartis: Consultancy, Research Funding. Roboz: AbbVie, Agios, Amgen, Amphivena, Array Biopharma Inc., Astex, AstraZeneca, Celator, Celgene, Clovis Oncology, CTI BioPharma, Genoptix, Immune Pharmaceuticals, Janssen Pharmaceuticals, Juno, MedImmune, MEI Pharma, Novartis, Onconova, Pfizer, Roche Pharmace: Consultancy; Cellectis: Research Funding. Mims: Novartis: Honoraria. Pollyea: Takeda, Ariad, Alexion, Celgene, Pfizer, Pharmacyclics, Gilead, Jazz, Servier, Curis: Membership on an entity's Board of Directors or advisory committees; Agios, Pfizer: Research Funding. Altman: Syros: Consultancy; NCCN: Other: Educational speaker; BMS: Consultancy; Celgene: Consultancy; Astellas: Consultancy; Ceplene: Consultancy; Janssen Pharmaceuticals: Consultancy; Novartis: Consultancy; ASH: Other: Educational speaker. Collins: Celgene Corporation: Research Funding; Agios: Research Funding; Arog: Research Funding; BMS: Research Funding. Mannis: Curis: Honoraria; Juno: Research Funding; Agios: Research Funding; Amgen: Honoraria. Uy: GlycoMimetics: Consultancy; Novartis: Consultancy, Other: Travel Suppport; Boehringer Ingelheim: Consultancy. Fathi: Juno: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Medimmune: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees. Stein: Amgen: Consultancy, Speakers Bureau; Stemline: Consultancy. Erba: Celgene: Consultancy, Other: Chair, Scientific Steering Committee , Speakers Bureau; Incyte: all research support paid to University of Alabama, Consultancy, Speakers Bureau; Jazz: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Amgen: Consultancy, Other: all research support paid to University of Alabama, Research Funding; Daiichi Sankyo: Consultancy, Other: all research support paid to University of Alabama, Research Funding; ImmunoGen: Consultancy, Other: all research support paid to University of Alabama, Research Funding; MacroGen: Consultancy; Ono: Consultancy; Pfizer: Consultancy; Seattle Genetics: Consultancy, Other: all research support paid to University of Alabama, Research Funding; Sunesis: Consultancy; Millennium/Takeda: Consultancy, Other: all research support paid to University of Alabama, Research Funding; Agios: Other: all research support paid to University of Alabama, Research Funding; Juno: Other: all research support paid to University of Alabama, Research Funding; Astellas: Other: all research support paid to University of Alabama, Research Funding; Celator: Other: all research support paid to University of Alabama, Research Funding; Janssen: Other: all research support paid to University of Alabama, Research Funding; Glycomimetics: Other: Chair, Data and Safety Monitoring Committee. Traer: ImmunoGen: Consultancy; Tolero: Consultancy; Notable Labs: Equity Ownership. Stuart: Pharmacyclics LLC, an AbbVie Company: Research Funding; Amgen: Consultancy, Honoraria; Agios: Research Funding; Celator/Jazz: Research Funding; Sunesis: Consultancy, Honoraria, Other: Travel Support, Research Funding; Bayer: Research Funding; Novartis: Research Funding; Incyte: Research Funding; ONO: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; MedImmune: Research Funding; Cantex: Research Funding; Astellas: Research Funding. Arellano: Cephalon Oncology: Research Funding. Sekeres: Celgene: Membership on an entity's Board of Directors or advisory committees. Yen: Agios: Employment, Equity Ownership. Kapsalis: Agios: Employment, Equity Ownership. Liu: Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Goldwasser: Agios: Employment, Equity Ownership. Agresta: Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Attar: Agios: Employment, Equity Ownership. Stone: Novartis: Consultancy; Celgene: Consultancy; Amgen: Consultancy; Abbvie: Consultancy; Fuji Film: Consultancy; Jazz: Consultancy; Astellas: Consultancy; Pfizer: Consultancy; Arog: Consultancy; Ono: Consultancy; Agios: Consultancy; Sumitomo: Consultancy. Kantarjian: ARIAD: Research Funding; Bristol-Meyers Squibb: Research Funding; Delta-Fly Pharma: Research Funding; Amgen: Research Funding; Pfizer: Research Funding; Novartis: Research Funding.

AbstractBackgroundMargins in transoral surgery for tonsil cancer can be limited by oropharyngeal wall thickness (OWT), but the normal range is not well established.MethodsIn 240 noncancer subjects, OWT was measured bilaterally in the vicinity of the tonsils with MRI. Statistical analysis was performed to assess for interaction of age, sex, location, and obesity.ResultsMean(SD) OWT measured 3.4(0.6) mm posteriorly, 3.7(2.0) mm between the styloglossus and stylopharyngeus, and 5.3(0.8) mm laterally. OWT was greater in men, correlated with obesity, decreased posteriorly and laterally in the 60–80 versus 40–59 year age groups, and increased when styloglossus/stylopharyngeus were closer. OWT was <5 mm in 36.7%–97.9% of locations, with the largest percentage below this threshold located posteriorly.ConclusionsOWT is frequently <5 mm, particularly in the posterior and intermuscular areas, suggesting that a smaller surgical margin may need to be accepted in transoral tonsil cancer surgery for anatomic reasons.

AbstractObjectiveTo describe the presentation and outcomes of patients with adrenal ganglioneuromas (AGNs).DesignSingle‐centre retrospective cohort study (1 January 1995 to 31 December 2019) and systematic review of literature (1 January 1980 to 19 November 2019).PatientsDiagnosed with histologically confirmed AGN.MeasurementsBaseline clinical, imaging and biochemical characteristics, recurrence rates and mortality. Subgroup analysis was performed on tumours with histologic elements of ganglioneuroma and pheochromocytoma (ie composite tumours).ResultsThe cohort study included 45 patients with AGN, 20 (44%) of which had composite tumours. Compared to pure AGN, patients with composite tumour were older (median age, 62.5 vs. 35 years, p < .001), had smaller tumours (median size, 3.9 vs. 5.7 cm, p = .016) and were discovered incidentally less frequently (65% vs. 84%, p = .009). No recurrences or ganglioneuroma‐specific mortality occurred during follow‐up (range, 0–266 months). The systematic review included 14 additional studies and 421 patients. The mean age of diagnosis was 39 years, and 47% were women. AGNs were discovered incidentally in 72% of patients, were predominantly unilateral (99%) and had a mean diameter of 5.8 cm and an unenhanced computed tomography (CT) attenuation of −118 to 49 Hounsfield units (HU). On imaging, 69% of AGNs were homogenous, 41% demonstrated calcifications, and 40% were lobulated.ConclusionsAGNs are rare benign tumours that present with variable imaging features including large size, unenhanced CT attenuation >20 HU, calcifications and lobulated shape. Imaging characteristics can assist in establishing a diagnosis and avoiding an unnecessary adrenalectomy. The association of pheochromocytomas with AGNs is frequent. Diagnosis should include biochemical testing.

Introduction: Patients with acute myeloid leukemia (AML) are often treated with intensive induction chemotherapy to achieve complete remission (CR). Early response to standard anthracycline plus cytarabine induction (7+3) is assessed by a day 14 nadir bone marrow biopsy. The nadir marrow has limitations, though, including sampling issues and ambiguity as to whether blasts are leukemia cells vs. regenerating marrow. In prior studies, the predictive value for remission of the nadir marrow is only 67-84%. A more accurate predictor of residual disease (RD) would give clinicians an opportunity to modify therapy earlier. Positron emission tomography (PET/CT) with 3'-deoxy-3'-[18F]fluorothymidine (FLT) is a molecular imaging modality that can assess cellular proliferation in the bone marrow compartment. A prior single-institution pilot study showed a significant difference in the marrow FLT uptake between patients with AML who achieved CR and those who had RD after count recovery. Methods: EAI141 was an ECOG-ACRIN-led, prospective, multi-center study designed to assess FLT PET/CT as a predictor of CR after AML induction. The primary objective was to evaluate the predictive value of post-treatment FLT PET/CT imaging for detecting RD, with the secondary objectives of evaluating the predictive value for detecting CR and estimating the sensitivity and specificity. Maximum standardized uptake value (SUVmax) of &gt; 7 g/mL in total bone marrow compartment was chosen prospectively based on data from a pilot study as a marker for presence of leukemia cells at nadir. The predictive values, sensitivity, and specificity of the FLT PET/CT and the nadir bone marrow biopsy were calculated. Eligible subjects were 18 years or older with previously untreated AML who were to receive induction with 7+3. Subjects underwent a nadir marrow biopsy and an FLT PET/CT scan 10-17 days after starting induction, and prior to any re-induction if disease was noted on the nadir marrow. A recovery marrow was performed 28-35 days after initial treatment or re-induction to assess CR or RD. Subjects could undergo an optional pre-treatment scan. Relapse-free survival (RFS) and overall survival (OS) were additional clinical outcomes. Results: 87 subjects from 9 centers were enrolled between 2016-2018, and 61 were considered evaluable. Reasons for being not evaluable included study ineligibility (n=3), no post-treatment scan (n=13), and no remission marrow (n=10). Median age was 58 years (range 21-73); 56% were men and 44% were women. CR was achieved in 56% (34/61). Treatment was a single induction course in 79% (48/61) and re-induction in 21% (13/61). Predictive value based on FLT PET/CT was 60% (9/15, 95% CI 32%-84%) for RD and 61% (28/46, 95% CI 45%-75%) for CR. Of patients who achieved CR, 28/34 had SUVmax ≤ 7 g/mL (sensitivity of 82%) and 9/27 of those who did not had high SUVmax &gt; 7 g/mL (specificity 33%). Predictive value of an aplastic marrow was 59% (26/44) for CR and 56% (9/16) for RD. Of patients who achieved CR, 26/33 had marrow hypoplasia (sensitivity 79%) and 9/27 with RD had disease in the nadir marrow (specificity 33%). Significant heterogeneity of bone marrow compartment post treatment (SUVhetero ranging from 0.24 to 1.07) was observed in FLT-PET/CT scans. Heterogeneity of bone marrow compartment decreased about 50% from pre-treatment to post-treatment FLT PET/CT. OS for all participants, stratified by post-treatment FLT PET/CT response and nadir marrow results, are summarized in the Figure. Conclusions: Although this study did not show significant advantage of FLT PET/CT compared to nadir marrow to predict RD or CR on the average, it did show signal heterogeneity in the study population that may be relevant to disease biology not appreciated by a single sampling site for the nadir or remission marrow. For example, in patients with false negative nadir biopsy, in approximately 20% of patients assessment with FLT PET/CT was correct, likely reflecting bone marrow heterogeneity and limitation of a single point sampling. Similarly, in almost 60% of patients with false positive nadir biopsy, FLT PET/CT assessment was correct. Figure 1 Disclosures Jeraj: AIQ Solutions: Current equity holder in private company. Kostakoglu:F. Hoffmann-La Roche: Consultancy. Strickland:KiTE: Consultancy; Kura: Consultancy; Astellas: Consultancy; Jazz: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Sunesis: Research Funding; ArcherDx: Consultancy; AbbVie: Consultancy. Uy:Daiichi Sankyo: Consultancy; Pfizer: Consultancy; Agios: Consultancy; Genentech: Consultancy; Jazz Pharmaceuticals: Consultancy; Astellas Pharma: Honoraria. Perlman:GE Healthcare: Research Funding; AIQ: Research Funding.