Abstract: Introduction: Racial and ethnic disparities exist in three areas related to hematopoietic cell transplantation (HCT): donor availability, access, and post-HCT outcomes. A significant barrier to access to HCT for patients (pts) of racial or ethnic minorities (REM) is the limited availability of fully matched donors (i.e., grafts matched at HLA-A, -B, -C, and -DRB1 loci) in volunteer registries. While mismatched unrelated donor (MMUD) grafts (i.e., & lt;7/8 match) can be offered to pts without matched donors, MMUD HCT results in poor survival when traditional graft-versus-host disease (GVHD) prophylaxis (PPx) is used. GVHD PPx with post-transplantation cyclophosphamide (PTCy) is associated with favorable survival after haploidentical HCT, and promising outcomes have been reported in a prospective multicenter study utilizing PTCy in MMUD HCT. Herein, we analyzed the outcomes of an ethnically diverse cohort of pts who underwent MMUD HCT with PTCy at two large urban transplant centers. Objectives and Methods: Subjects receiving HCT from an MMUD from 2010-to 2020 at the University of Miami and Memorial Sloan-KetteringCancer Center were included. Pts were stratified by age, HCT indication, race/ethnicity, graft type, conditioning intensity, disease status, and degree of HLA mismatch. The primary study endpoint was one-year overall survival (OS). Secondary endpoints were event-free survival (EFS), non-relapse mortality (NRM), and cumulative incidence of acute and chronic GVHD. Results: A total of 82 pts were evaluated. The median age at HCT was 60 years (21-75), the most common indication for HCT was acute leukemia (51%), 41% of pts received an ablative conditioning regimen, and 50% received peripheral blood (PB) grafts. Forty-four percent identified as non-Hispanic white (NHW), and 56% identified as REM (Non-Hispanic Black: 30%; Hispanic: 64%; Asian/Pacific: 4.3%). The two groups (NHW vs. REM) were well-matched for leading HCT indication, disease-risk index, degree of mismatch, and disease status at HCT. REM pts were younger (median age at HCT 65 vs 56 years for NHW, p=0.001) and more likely to receive a PB graft (63% vs 40%, P = 0.04). One-year OS was 75%, EFS was 69%, and NRM was 16% for the entire cohort. Grade 3-4 acute GVHD at day 180 post-HCT was 15%, and one-year severe chronic GVHD was 9%. OS was comparable between 7/8-matched and highly-mismatched ( & lt;6/8) HCT recipients (75% vs. 76%, respectively; P & gt;0.9). There were no differences in one-year OS (77% vs 74%, p = 0.9) and EFS (63% vs 72%, p = & gt;0.9) between NHW and REM pts. Similarly, rates of acute (17% vs 13%, p = 0.5) and chronic GVHD (5.7% vs 11%, p = 0.5) were comparable between NHW and REM pts. Conclusion: PTCy resulted in encouraging clinical outcomes following MMUD HCT. Post-HCT OS, RFS, and GVHD rates were comparable between NHW and REM pts and those receiving 7/8 or highly mismatched grafts. Favorable post-HCT outcomes following MMUD with PTCy may increase HCT utilization and access for REM pts. Citation Format: Antonio M. Jimenez Jimenez, Sunil Iyer, Krishna Komanduri, Samantha Brown, Trent Wang, Stephanie Chinapen, Denise Pereira, Sean Devlin, Mark Goodman, Amer Beitinjaneh, Craig Sauter, Lazaros Lekakis, Miguel Angel Perales, Doris Ponce, Brian Shaffer. HLA-mismatched unrelated donor hematopoietic cell transplantation with post-transplant cyclophosphamide improves clinical outcomes for racial and ethnic minority patients with hematologic malignancies [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr B121.

Abstract: Background: Patients with TP53 MUT MDS/AML experience poor clinical outcomes with high rates of disease recurrence and short overall survival (OS). Characterization of these individuals' post-HCT mortality is uniquely challenging due to competing risks from disease relapse and treatment toxicity. Transplant registries contain high-level outcomes data, however, there is a lack of detailed data in molecularly defined subsets of diease. This analysis was undertaken to bridge this gap. Methods: Allogeneic HCT recipients between 1/2014 and 12/2018 were retrospectively studied. Key inclusion criteria were TP53 MUT by NGS or deletion of chromosome 17/17p by FISH/cytogenetics. The primary outcome of non-relapse mortality (NRM) was defined as death from any cause other than disease with relapse as competing risk. Secondary outcomes for this analysis were OS, cumulative incidence of relapse (CIR), and relapse free survival (RFS). Relapse was defined as relapse/progression with NRM as competing risk. Results: 384 TP53 MUT MDS/AML patients were analyzed. 55% of patients were transplanted for AML, 41% received myeloablative conditioning (MAC), 39% had secondary MDS/AML, and 26% received prior chemo and/or radiation therapy (XRT). Median time from HCT to last follow-up was 321 days (range 8-2,385 days). Mutational data was available in 264 patients and cytogenetic data was available in 368 patients; 78% of patients had a complex karyotype (CK), 82% had TP53 missense mutations, and 74% had bi-allelic targeting of the TP53 gene. The incidence of all-grade acute and chronic GVHD (cGVHD) was 52% and 31%, respectively. One and 2 year OS was 48.5% and 30.9%, respectively. Estimated CIR at 1 and 2 years was 49% and 54.9%, respectively. The 1 year NRM was 13.7% and 2 year NRM was 18.1%. In multivariate analysis (MVA), there was no association between NRM and the clinical, molecular, or genetic features of TP53 MUT MDS/AML. HCT diagnosis of MDS (HR: 0.67, 95% CI: 0.46-0.97, p: 0.036), mono-allelic TP53 MUT (HR: 0.6, 95% CI: 0.39-0.94, p: 0.023), achievement of full donor PB chimerism (HR: 0.33, 95% CI: 0.14-0.85, p: 0.022), BM chimerism (HR: 0.33, 95% CI: 0.18-0.60, p: 0.003), and cGVHD (HR: 0.35, 95% CI: 0.23-0.51, p: & lt;0.001) correlated with lower rates of relapse while CK predicted for increased relapse (HR: 2.5, 95% CI: 1.49-4.19, p: 0.001). Inferior OS was associated with CK (HR: 1.84, 95% CI: 1.19-2.85, p: 0.006) and history of prior chemo/XRT (HR: 1.84, 95% CI: 1.01-1.93, p: 0.006) whereas high KPS (HR: 0.98, 95% CI: 0.97-1, p: 0.046), mono-allelic TP53 mutations (HR: 0.52, HR: 0.36-0.77, p: 0.001), full donor PB chimerism (HR: 0.36, 95% CI: 0.19-0.68, p: 0.002), BM chimerism (HR: 0.3, 95% CI: 0.19-0.49, p: & lt;0.001), and cGVHD (HR: 0.36, 95% CI: 0.18-0.36, p: & lt;0.001) were associated with improved OS. In subgroup analysis, history of chemo and/or XRT increased NRM in AML (HR: 4.24, 95% CI: 1.35-13.39, p: 0.014). Pre-HCT TP53 MUT persistence by NGS (HR: 3.59, 95% CI: 1.43-9, p: 0.007) predicted for post-HCT relapse whereas pre-HCT CR (HR: 2.93, 95% CI: 1.54-5.59, p: 0.001) and full donor BM chimerism (HR: 0.14, 95% CI: 0.05-0.38, p: & lt;0.001) were associated with lower rates of relapse. High KPS (HR: 0.96, 95% CI: 0.98-0.99, p: 0.021) and cGVHD (HR: 0.3, 95% CI: 0.16-0.56, p: & lt;0.001) corresponded with improved OS. Prior chemo/XRT was associated with shorter OS (HR: 2.11, 95% CI: 1.06-4.18, p: 0.033) No significant NRM associations were identified in MDS. CK (HR: 5.04, 95% CI: 1.95-13.01, p: & lt;0.001) and RIC/NMA conditioning intensity (HR: 2.54, 95% CI: 1.26-5.1, p: 0.009) increased risk of post-HCT relapse while full donor BM chimerism (HR: 0.15 95% CI: 0.08-0.31, p: & lt;0.001), full donor PB chimerism (HR: 0.17, 95% CI: 0.17, p: & lt;0.001), and cGVHD (HR: 0.17, 95% CI: 0.07-0.42, p: & lt;0.001) reduced this risk. OS was improved with mono-allelic mutations (HR: 0.54, 95% CI: 0.32-0.96, p: 0.034), full donor BM (HR: 0.24, 95% CI: 0.12-0.71, p: & lt;0.001), PB (HR: 0.29, 95% CI: 0.09-0.3, p: 0.007) chimerism, and cGVHD (HR: 0.16, 95% CI: 0.09-0.3, p: & lt;0.001). Conclusions: From this large multi-institutional cohort of TP53 MUT myeloid neoplasms, we report a low NRM rate, likely due to high rates of post-HCT relapse/progression. These data demonstrate associations between bi-allelic TP53m/CK and post-HCT outcomes. Our work highlights the importance donor chimerism after HCT and provides new understanding of the importance of chronic GVHD in TP53 MUT MDS/AML. Figure 1 Figure 1. Disclosures Byrne: Karyopharm: Research Funding. Logan: Amgen, Pfizer, AbbVie: Consultancy; Pharmacyclics, Astellas, Jazz, Kite, Kadmon, Autolus, Amphivena: Research Funding. Lee: CareDx: Membership on an entity's Board of Directors or advisory committees; Kadmon: Membership on an entity's Board of Directors or advisory committees; Kite: Membership on an entity's Board of Directors or advisory committees; Fresensius Kabi: Consultancy; Jazz,: Consultancy; Incyte: Research Funding. Goodman: Seattle Genetics: Consultancy, Speakers Bureau; EUSA Pharma: Consultancy, Honoraria. Gill: Interius Biotherapeutics: Current holder of stock options in a privately-held company, Research Funding; Novartis: Other: licensed intellectual property, Research Funding; Carisma Therapeutics: Current holder of stock options in a privately-held company, Research Funding. Jimenez: Takeda: Research Funding; AbbVie: Research Funding. Metheny: Pharmacosmos: Honoraria; Incyte: Speakers Bureau. Bhatnagar: Pfizer: Honoraria; Celgene: Honoraria; Novartis: Honoraria; Astellas: Honoraria; Cell Therapeutics: Honoraria, Research Funding; Kite: Honoraria; Karyopharm: Honoraria, Research Funding; Sumitomo Dainippon Pharma: Research Funding. Hamilton: Syndax: Membership on an entity's Board of Directors or advisory committees; Equilium: Membership on an entity's Board of Directors or advisory committees. Mishra: Novartis: Research Funding. Savona: BMS-Celgene: 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; 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; 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.

Abstract: Introduction Allogeneic hematopoietic stem cell transplant (allo-SCT) is the only curative treatment modality for patients with CMML. Here we retrospectively reviewed the data for patients with CMML who received an all-SCT at our institution to identify factors associated with improved survival and determine whether treatment with hypomethylating agents (HMA) before transplant improves survival for these patients. Methods All 83 patients 18 years of age or older with a diagnosis of CMML confirmed at The University of Texas MD Anderson Cancer Center who underwent allo-SCT between April 1991 and December 2013 were identified through review of the institutionÕs medical records and included in this analysis. Forty, 7, and 36 patients had CMML-1, CMML-2 and CMML that had progressed to AML (CMML/AML) respectively. The median age was 57 years. CMML specific cytogenetic risk at diagnosis (Such E, hematologica, 2011) was good, intermediate, and high risk in 46, 19, and 18 patients respectively. Seventy-eight patients received induction treatment before transplant, 37 receiving HMA (either 5-azacytidine or decitabine) for at least 3 courses and 41 receiving 1-2 courses of cytotoxic chemotherapy. Among the patients who received induction therapy, 15 patients in HMA group and 9 patients in convention chemotherapy group achieved a complete remission before transplant. Thirty, 47 and 6 patients received transplants from matched related donors (MRD), matched unrelated donors (MUD), and mismatched related or unrelated donors (MMD), respectively. The sources of hematopoietic stem cells were peripheral blood for 48 patients (57.8%) and bone marrow for 35 patients (42.2%). Conditioning regimens varied; most patients received either fludarabine in combination with busulfan or fludarabine combined with melphalan. Sixty-four patients received myeloablative and 19 patients received reduced intensity conditioning regimens. Graft-versus-host disease (GVHD) prophylaxis consisted of tacrolimus and methotrexate. Patient and transplant characteristics did not significantly differ between the patients treated with HMA and the patients treated with conventional chemotherapy or given supportive care alone. The primary endpoint was progression-free survival (PFS). The secondary endpoints were overall survival (OS), Treatment related mortality (TRM), relapse incidence through last follow-up and incidences of acute GVHD and chronic GVHD. All of these outcomes were measured from the time of allo-SCT. Results Median follow up duration for 29 survivors was 48 months. Seventy-five patients engrafted (90.4%) with median time to neutrophil and platelet engraftment of 13 and 15 days respectively. Patients treated with a HMA had a significantly lower cumulative incidence (CI) of relapse at 3 years post-transplant (22%) than those treated with other agents (35%; p=0.03), whereas TRM at 1 year post-transplantdid not significantly differ between the groups (27% and 30%, respectively; p=0.84). Acute GVHD all grades and grade 2-4 were seen in 28.2% versus 35.8% (p=0.05) and 12.8% versus 11.3% (p=0.72) in patients who received a HMA compared to those who treated with other agents respectively. CI of chronic GVHD was 35% in patients treated with a HMA versus 19.2% in those treated with other agents (p=0.36) while CI of chronic extensive GVHD was seen in only 26.7% versus 19.2% respectively (p=0.64). The lower relapse rate resulted in a significantly higher 3-year PFS rate in patients treated with a HMA (43%) than in those who received other treatments (27%; p=0.04) (Figure 1). However, therapy with HMA before transplant did not significantly influence the 3-year OS rate (45% in those treated with HMA and 39% in those treated with other agents; p=0.22). The independent prognostic factors for PFS were a blast count of 〈 5% before transplant (HR 0.36, 95%CI 0.14-0.78), treatment with a HMA (HR 0.44, 95% CI 0.23-0.86), a transplant from an MRD (HR 0.41, 95% CI 0.22-0.94), development of grade 2-4 acute GVHD (HR 2.7, 95% CI 1.27-5.77), and development of chronic GVHD (HR 0.15, 95% CI 0.05-0.45). Conclusion We conclude that treatment with hypomethylating agents before allo-SCT may improve survival in patients with CMML. Figure 1. Progression free survival Figure 1. Progression free survival Disclosures Alousi: Therakos, Inc: Research Funding. Andersson:Otsuka Research and Development, Inc.: Consultancy.

Abstract: The current standard of care to prevent graft versus host disease (GVHD) after HLA mismatched unrelated donor (URD) allogeneic hematopoietic cell transplantation (HCT) is tacrolimus, methotrexate (MTX) and anti-thymocyte globulin (ATG). Recently, an approach based on administration of post-transplant cyclophosphamide (PT-Cy) demonstrated promise in a prospective trial for HLA mismatched URD HCT. Here, we compared tacrolimus/MTX/ATG (ATG group) treatment, with that of PT-Cy, mycophenolate mofetil, and tacrolimus or sirolimus (PT-Cy group) after HLA mismatched URD HCT, at two academic centers with similar peri-transplant supportive care practices. Subjects that underwent HCT from a URD mismatched at one or more loci among HLA-A, -B, -C, and -DRB1 from 2010-2020 were included. The primary endpoint of our study was one-year GVHD-free, relapse-free survival (GRFS). Of 128 total subjects included (ATG: 46; PT-Cy: 82), the median age was 54.7 (range: 21.0 - 72.0) in the ATG group and 60.3 (21.0 - 75.2) in the PT-Cy group. Notably, 74 subjects (57.8%) belonged to a racial/ethnic minority, while 53 (41.4%) received a bone marrow (BM) graft, and 26 (20.3%) received a highly mismatched (i.e., & lt;6/8 HLA) graft. A higher proportion of PT-Cy subjects received BM (50% vs. 26.1%, P= 0.01) and highly mismatched grafts (30.5% vs. 2.2%, P=0.001). The groups were well matched for key demographic data, including indication for HCT, high-risk disease, and HCT comorbidity index. The rate of primary neutrophil engraftment at day 28 post HCT was similar between the two groups: 91% (83%-99%), in the ATG group, and 90% (84%-97%), in the PT-Cy group. The median day of neutrophil engraftment was +17 in the ATG, and +20 in the PT-Cy groups. Platelet engraftment at day 100 was 84.8% (74.4% - 95.2%) and 86.6% (79.2% - 94%) in the ATG and PT-Cy groups, respectively. Among subjects that survived 3-months post HCT and had donor chimerism testing, full donor chimerism (≥95% donor) was achieved in 24/26 (92.3%) patients in the ATG group, and 61/68 (89.7%) subjects in the PT-Cy group. Overall, the one-year GRFS was 16% (95% confidence interval: 8% - 31%) vs. 54% (44% - 66%, p & lt; 0.001) in the ATG and PT-Cy groups, respectively. The adjusted, multivariate hazard ratio (HR) for GRFS was 0.34 (0.21 - 0.55, p & lt; 0.001), in association with the use of PT-Cy. The one-year overall survival (OS) in the ATG group was 45% (32% - 62%) vs. 75% (66% - 85%, p & lt; 0.001) in the PT-Cy group. There was no difference in 2-year relapse incidence (27%, 14-39% vs. 19%, 10% - 28%, p = 0.2), whereas 1-year non-relapse mortality (NRM) was increased with ATG-based prophylaxis: (38%, 23% - 52% vs. 16%, 9% - 25%, p = & lt;0.001). The use of PT-Cy was associated with improved GRFS for patients treated with BM (HR = 0.27, 0.11 - 0.62; p = 0.002) and G-CSF mobilized, peripheral blood derived (PB) grafts (HR = 0.39, 0.21 - 0.71; p = 0.002). BM grafts were not an independent predictor of GRFS (HR: 1.2, 0.8 - 1.9; p = 0.5) in a multivariate Cox regression model. The use of PT-Cy, compared to ATG, was associated with lower rates of grade 3-4 acute GVHD in the entire cohort (ATG: 22%, 18% - 45% vs. PT-Cy: 15%, 8% - 23%; p = 0.03), and in the sub-cohorts of patients transplanted with PB (ATG: 33%, 17% - 49% vs. PT-Cy: 20%, 9% - 33%) and BM grafts (ATG: 25%, 1% - 50% vs. PT-Cy: 10%, 1% - 19%). Chronic GVHD requiring systemic immune suppression was more frequent in the ATG/PB group (26%, 13% - 42%) than in the ATG/BM (8%, 0% - 24%), the PT-Cy/PB (8%, 2% - 19%), and the PT-Cy/BM (10%, 1% - 19%) groups. Despite greater HLA-mismatching, PT-Cy following mismatched URD HCT resulted in superior GRFS, OS and lower NRM and GVHD rates compared to ATG-based GVHD prophylaxis. These results indicate that PT-Cy is the preferred method to prevent GVHD after mismatched URD HCT and confers a benefit in patients treated with either PB or BM-derived allografts. Combinatorial approaches, using the T-cell co-stimulatory blockading agent abatacept, in addition to tacrolimus/methotrexate, may also prevent GVHD in this population, and can be compared to a PT-Cy-based approach in a prospective clinical trial. Figure 1 Figure 1. Disclosures Jimenez: AbbVie: Research Funding; Takeda: Research Funding. Perales: MorphoSys: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria; Karyopharm: Honoraria; Merck: Honoraria; Equilium: Honoraria; Miltenyi Biotec: Honoraria, Other; Medigene: Honoraria; Kite/Gilead: Honoraria, Other; Incyte: Honoraria, Other; Cidara: Honoraria; Takeda: Honoraria; Nektar Therapeutics: Honoraria, Other; Servier: Honoraria; Sellas Life Sciences: Honoraria; Omeros: Honoraria; NexImmune: Honoraria; Novartis: Honoraria, Other. Sauter: Precision Biosciences: Consultancy; Genmab: Consultancy; Celgene: Consultancy, Research Funding; Kite/Gilead: Consultancy; Bristol-Myers Squibb: Research Funding; GSK: Consultancy; Gamida Cell: Consultancy; Novartis: Consultancy; Spectrum Pharmaceuticals: Consultancy; Juno Therapeutics: Consultancy, Research Funding; Sanofi-Genzyme: Consultancy, Research Funding. Beitinjaneh: Kite/Gilead: Other: Ad Board Event Attendee. Ponce: CareDx: Consultancy, Honoraria; Ceramedix: Consultancy, Honoraria; Seres Therapeutics: Consultancy, Research Funding; Kadmon pharmaceuticals: Consultancy, Honoraria; Takeda Pharmaceuticals: Research Funding; Generon Pharmaceuticals: Consultancy. OffLabel Disclosure: Off-label use of Cyclophosphamide for Graft-versus-Host Disease prevention will be discussed in the abstract.