Abstract: Busulfan is an alkylating drug routinely used in conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT). A myeloablative conditioning regimen, including busulfan, is commonly used in patients undergoing T-cell depletion (TCD) and allo-HCT, but data on optimal busulfan pharmacokinetic (PK) exposure in this setting are limited. Between 2012 and 2019, busulfan PK was performed to target an area under the curve exposure between 55 and 66 mg × h/L over 3 days using a noncompartmental analysis model. We retrospectively re-estimated busulfan exposure following the published population PK (popPK) model (2021) and correlated it with outcomes. To define optimal exposure, univariable models were performed with P splines, wherein hazard ratio (HR) plots were drawn, and thresholds were found graphically as the points at which the confidence interval crossed 1. Cox proportional hazard and competing risk models were used for analyses. 176 patients were included, with a median age of 59 years (range, 2-71). Using the popPK model, the median cumulative busulfan exposure was 63.4 mg × h/L (range, 46.3-90.7). The optimal threshold was at the upper limit of the lowest quartile (59.5 mg × h/L). 5-year overall survival (OS) with busulfan exposure ≥59.5 vs & lt;59.5 mg × h/L was 67% (95% CI, 59-76) vs 40% (95% CI, 53-68), respectively (P = .02), and this association remained in a multivariate analyses (HR, 0.5; 95% CI, 0.29; 0.88; P = .02). In patients undergoing TCD allo-HCT, busulfan exposure is significantly associated with OS. The use of a published popPK model to optimize exposure may significantly improve the OS.

Abstract: CD19-targeted chimeric antigen receptor (CAR) T-cell therapy has become a breakthrough treatment of patients with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). However, despite the high initial response rate, the majority of adult patients with B-ALL progress after CD19 CAR T-cell therapy. Data on the natural history, management, and outcome of adult B-ALL progressing after CD19 CAR T cells have not been described in detail. Herein, we report comprehensive data of 38 adult patients with B-ALL who progressed after CD19 CAR T therapy at our institution. The median time to progression after CAR T-cell therapy was 5.5 months. Median survival after post–CAR T progression was 7.5 months. A high disease burden at the time of CAR T-cell infusion was significantly associated with risk of post–CAR T progression. Thirty patients (79%) received salvage treatment of post–CAR T disease progression, and 13 patients (43%) achieved complete remission (CR), but remission duration was short. Notably, 7 (58.3%) of 12 patients achieved CR after blinatumomab and/or inotuzumab administered following post–CAR T failure. Multivariate analysis revealed that a longer remission duration from CAR T cells was associated with superior survival after progression following CAR T-cell therapy. In summary, overall prognosis of adult B-ALL patients progressing after CD19 CAR T cells was poor, although a subset of patients achieved sustained remissions to salvage treatments, including blinatumomab, inotuzumab, and reinfusion of CAR T cells. Novel therapeutic strategies are needed to reduce risk of progression after CAR T-cell therapy and improve outcomes of these patients.

Abstract: Abstract 4954 Background Multiple Myeloma (MM) remains incurable with current approaches and newer therapies targeting the abnormal disease biology need to be developed. The malignant plasma cell is highly dependent on the marrow microenvironment, which promotes tumor cell proliferation as well as survival. There is increased bone marrow vascular density in patients with MM and the degree of neo-angiogenesis appear to be prognostic in this disease. Studies have also shown that vascular endothelial growth factor (VEGF) is intricately involved in the interaction between the marrow microenvironment and the myeloma cell. These findings suggested that the VEGF pathway may be a valuable target for therapeutic approach in this disease. Patients and Methods We designed a phase 2 trial of Sunitinib in patients with relapsed multiple myeloma who had received less than three prior therapies. Sunitinib malate (SU11248; Sutent) is a novel, multi-targeted, small molecule inhibitor of the receptor tyrosine kinases (RTKs), including vascular endothelial growth factor receptor-1 (VEGFR-1), -2, and -3, and platelet-derived growth factor receptor (PDGFR) -α and -β. The treatment consisted of Sunitinib 37.5 mg given daily in a continuous fashion in six-week cycles. Toxicities were graded according to CTCAE response version 3.0 and responses were assessed according to the International Myeloma Working Group consensus criteria. Response rate of single agent Sunitinib was the primary endpoint of the study. Results 13 patients were accrued between July of 2007 and April 2009 before the study was closed. The median age of the study population was 61 years (range, 53 - 84), and included nine females (69%). The median time from diagnosis to registration was 39.2 months (range, 4.5 - 88) and 10 patients had received previous stem cell transplant. Previous therapy included lenalidomide in 7 patients, thalidomide in 5 patients and bortezomib in 2 patients. All 13 patients were alive at last follow up with a median follow-up of 11.2 months (range, 1.3 -21.2). All patients have gone off study, disease progression being the most common cause (9 patients), followed by adverse events (3 pts) and alternate treatment in the remaining patient. A hematological grade 3 or higher adverse event was documented in 6 patients and a grade 3 or higher non-hematological adverse event was seen in 8 patients. A grade 3 or higher neutropenia was observed in 5 pts and thrombocytopenia in 2 pts. Fatigue was common and was seen in 11 pts. The median number of cycles administered was one (range, 1-5) and the total number of cycles across 13 patients was 22. Treatment delays or interruptions were seen in five and six patients respectively. The most common reason for treatment delays was hematologic adverse events. No responses (PR or better) were seen, and stable disease was seen in eight of the 13 patients as the best response. The median time to progression was 2.9 months. Conclusions Single agent Sunitinib has no clinically relevant efficacy in this group of patients with relapsed myeloma with one or two previous therapies. Hematological toxicity was higher than anticipated. Whereas these results indicate that VEGFR TK inhibitors are not active in previously treated myeloma, it does not preclude the possibility that VEGF targeting strategies may enhance the efficacy of other therapies. Disclosures Kumar: CELGENE: Research Funding; MILLENNIUM: Research Funding; BAYER: Research Funding; GENZYME: Research Funding; NOVARTIS: Research Funding. Gertz:celgene: Honoraria; millenium: Honoraria, Membership on an entity's Board of Directors or advisory committees. Dispenzieri:Celgene: Research Funding.

Abstract: Background: Treatment of chronic myeloid leukemia (CML) with a tyrosine kinase inhibitor (TKI) offers significant improvements over previous treatments in terms of survival and toxicity yet has been associated with reduced health-related quality of life and very high cost. Discontinuing TKIs with regular monitoring is safe, but little is known about the impact of discontinuation on patient-reported outcomes (PROs). In the largest U.S. study to date, we evaluated molecular recurrence of CML and PROs after TKI discontinuation. Methods: The Life After Stopping TKIs (LAST) study was a prospective single-group longitudinal study. Key inclusion criteria were age & gt; 18 years, patient on TKI therapy (imatinib, dasatinib, nilotinib, or bosutinib) for & gt; 3 years with documented BCR-ABL & lt; 0.01% by PCR for & gt; 2 years, and no previous TKI resistance. We monitored disease outcome (PCRs by central lab) and PROs (PROMIS computerized adaptive tests via REDCap) monthly for the first 6 months, every 2 months until 24 months, then every 3 months until 36 months. Molecular recurrence was defined as & gt; 0.1% BCR-ABL IS by central lab (loss of major molecular response [MMR] ). We considered 3 points to be clinically meaningful and hypothesized that by 6 months after TKI discontinuation, fatigue, depression, sleep disturbance, and diarrhea would improve by at least 3 points each, corresponding to a standardized effect size of 0.3. Given reports of a withdrawal syndrome of musculoskeletal pain in some patients after discontinuation, pain was an additional outcome of particular interest. For each PRO domain, we estimated a polynomial piecewise linear mixed effects model that specified one nonlinear trajectory after TKI discontinuation and, for those with molecular recurrence, another trajectory after TKI restart. The models included patient-level random effects for the intercepts and linear slopes. Results: From 12/2014 to 12/2016, 172 patients enrolled from 14 U.S. sites. Median age was 60 years (range 21-86) and 89 (52%) were female. The median time on TKI prior to enrollment was 81 months (IQR 54-123). With a minimum follow-up of 24 months, 107 (62%) patients remained in a treatment free remission (TFR). Reasons for restarting therapy were: loss of MMR by central (n=56) or local (n=2) lab, patient decision (n=4), and withdrawal syndrome (n=3). Missing PRO data was minimal ( & lt; 5%) with & gt; 2000 assessments completed. For patients in TFR at 6 months, the average estimated improvement in fatigue was 2.6 points (95% CI 2.5-2.7), depression was 1.9 points (95% CI 1.8-1.9), sleep disturbance was 0.9 points (95% CI 0.8-1.0), and diarrhea was 2.7 points (95% CI 2.6-2.7). The average estimated worsening in pain interference (i.e., the extent to which pain affects daily life) was 0.4 points (95% CI 0.3-0.5). The figure shows the distribution of estimated change for each domain at 6 months. All patients showed improvements in depression, diarrhea, and fatigue. About 1 in 6 patients (17%) experienced a clinically meaningful (i.e., at least 3 points) improvement in fatigue and/or diarrhea at 6 months. Conclusion: The LAST study is the largest US TKI discontinuation study to date, and the first to include comprehensive PRO measurement. For patients in TFR at 6 months, TKI discontinuation conferred modest benefits in fatigue and diarrhea on average, with a negligible increase in pain interference. Some patients experienced more notable improvements in fatigue and diarrhea. Planned secondary analyses will include change over time up to 3 years and evaluation of additional PRO domains, including anxiety, physical function, social function, and sexual function. Our results provide important new evidence to support shared patient-provider clinical decision making regarding TKI discontinuation for patients with CML. Figure. Disclosures Radich: Novartis: Other: RNA Sequencing; TwinStrand Biosciences: Research Funding. Mauro:Pfizer: Consultancy; Takeda: Consultancy; Novartis Oncology: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy. Pinilla Ibarz:Sanofi: Speakers Bureau; Abbvie: Consultancy, Speakers Bureau; Teva: Consultancy; Janssen: Consultancy, Speakers Bureau; Novartis: Consultancy; Takeda: Consultancy, Speakers Bureau; Bayer: Speakers Bureau; TG Therapeutics: Consultancy; Bristol-Myers Squibb: Consultancy. Larson:Celgene: Consultancy; Novartis: Honoraria, Other: Contracts for clinical trials; Agios: Consultancy. Oehler:Blueprint Medicines: Consultancy; NCCN: Consultancy; Pfizer Inc.: Research Funding. Deininger:Humana: Honoraria; Incyte: Honoraria; Blueprint: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria, Research Funding; Ascentage Pharma: Consultancy, Honoraria; TRM: Consultancy; Sangoma: Consultancy; Fusion Pharma: Consultancy; Adelphi: Consultancy; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria; Sangamo: Consultancy. Shah:Bristol-Myers Squibb: Research Funding. Ritchie:Tolero: Other: Advisory board; Celgene: Other: Advisory board; Celgene, Novartis: Other: travel support; Jazz Pharmaceuticals: Research Funding; Celgene, Incyte, Novartis, Pfizer: Consultancy; AStella, Bristol-Myers Squibb, Novartis, NS Pharma, Pfizer: Research Funding; Ariad, Celgene, Incyte, Novartis: Speakers Bureau; Genentech: Other: Advisory board; Pfizer: Other: Advisory board, travel support; agios: Other: Advisory board. Silver:PharmEssentia: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Cortes:Sun Pharma: Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Forma Therapeutics: Consultancy, Honoraria, Research Funding; BiolineRx: Consultancy; Bristol-Myers Squibb: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding; Biopath Holdings: Consultancy, Honoraria; Immunogen: Consultancy, Honoraria, Research Funding; Merus: Consultancy, Honoraria, Research Funding; Astellas Pharma: Consultancy, Honoraria, Research Funding. Atallah:Jazz: Consultancy; Helsinn: Consultancy; Pfizer: Consultancy; Takeda: Consultancy, Research Funding; Jazz: Consultancy; Helsinn: Consultancy; Novartis: Consultancy.