Shen, Rhine R.

Cancer immunotherapy—including immune checkpoint inhibition (ICI) and adoptive cell therapy (ACT)—has become a standard, potentially curative treatment for a subset of advanced solid and liquid tumors. However, most patients with cancer do not benefit from the rapidly evolving improvements in the understanding of principal mechanisms determining cancer immune responsiveness (CIR); including patient-specific genetically determined and acquired factors, as well as intrinsic cancer cell biology. Though CIR is multifactorial, fundamental concepts are emerging that should be considered for the design of novel therapeutic strategies and related clinical studies. Recent advancements as well as novel approaches to address the limitations of current treatments are discussed here, with a specific focus on ICI and ACT.

Introduction: Brexu-cel is an autologous anti-CD19 CAR T-cell therapy approved in the US and EU for treatment of adults with R/R MCL (after ≥2 prior therapies in EU) based on a high objective response rate (ORR; 93%; 67% complete response [CR] rate) in pts who received the pivotal dose (2×106 anti-CD19 CAR T cells/kg; Cohort 1; N=60) in ZUMA-2 (NCT02601313; Wang et al, N Engl J Med 2020). After ~4 years (y) of median follow-up, Brexu-cel demonstrated a median overall survival (OS) of 46.4 months (mo) in 68 pts with R/R MCL in Cohort 1 (Goy et al. ASH 2023). Cohort 2 was established to assess a lower dose (0.5 x 106 anti-CD19 CAR T cells/kg); however, the risk/benefit ratio of the Cohort 1 dose was deemed the optimal dose before Cohort 2 reached full enrollment. Here we report primary outcomes of Cohort 2 and 5-y outcomes of Cohorts 1 and 2. Methods: Pts with R/R MCL and ≤5 prior therapies including a BTKi received optional bridging therapy (protocol-defined), lymphodepleting chemotherapy, and 1 infusion of brexu-cel. The primary endpoint was ORR (CR + partial response [PR]) per Lugano classification (Cheson et al. J Clin Oncol. 2014) by independent radiology review committee (IRRC) assessment. Key secondary endpoints were duration of response (DOR), best objective response (BOR), progression-free survival (PFS), OS, and safety. After ≥24 mo of assessment, pts could transition to long-term follow-up (LTFU), NCT05041309, where they were monitored for late-onset targeted/serious adverse events (AEs) possibly related to brexu-cel, presence of replication-competent retrovirus (RCR), and/or insertional mutagenesis. Descriptive statistics are reported herein. Results: As of the primary analysis data cutoff date, July 24, 2019, 17 pts enrolled in Cohort 2, 14 (82%) of whom were treated with brexu-cel with median follow-up of 16.0 mo (range, 13.9-18.0). Pt characteristics for Cohort 2 (N=14) were similar to Cohort 1; median (range) age and number or prior therapies was 61.5 y (52-73) and 3 (2-5); 100% US-treated, 79% male, 71% extranodal disease, 50% intermediate or high s-MIPI scores, 50% refractory to last therapy, and 43% had prior autologous stem cell transplantation. ORR was 93% (95% CI, 66.1-99.8) per IRRC; 64% had a CR (95% CI, 35.1-87.2), 29% had a PR (95% CI, 8.4-58.1) and 1 pt was not assessed. All 14 pts had ≥1 AE of any grade (Gr), with Gr ≥3 AEs occurring in 93% of pts; the most common being hypotension (50%), white blood cell count decrease (50%), anemia (43%), and neutrophil count decrease (43%). Rates of Gr ≥3 cytokine release syndrome (CRS) and neurological events were 7% and 43%, respectively. As of April 1, 2024, median follow-up (range) for Cohort 1 and 2 was 67.8 mo (58.2-88.6; N=68) and 72.3 mo (70.1-74.3; N=14), respectively. In Cohort 1, 24 pts were still alive (35%; 2 withdrew consent and 1 lost to follow up) and 44 pts died (65%). In Cohort 2, 8 pts were still alive (57%; 2 withdrew consent and 1 lost to follow up) and 6 pts died (43%). A total of 27 pts (Cohort 1, n=23; Cohort 2, n=4) enrolled in the LTFU study by data cutoff with a median follow-up time of 70.2 mo (range, 58.2-88.6). Median (95% CI) investigator-assessed DOR and PFS were 36.5 mo (17.7-48.9; n=60; 17 patients in ongoing response, all CR) and 25.3 mo (12.7-46.6; N=68) in Cohort 1; and 57.5 mo (4.7-not estimable [NE]; n=12; 3 pts in ongoing response, all CR) and 29.5 mo (3.3-NE; N=14) in Cohort 2. Median OS (95% CI) and 60-mo OS rates (95% CI) were 46.5 mo (24.9- 60.2) and 38.5% (26.7-50.1) in Cohort 1; and not reached (9.4-NE) and 53.6% (23.8-76.2) in Cohort 2. One pt had 3 ongoing AEs on LTFU, hypogammaglobulinemia and 2 viral infections that arose prior to LTFU. Two pts died on LTFU, both due to progressive disease; no new secondary malignancies or RCR cases were reported. Conclusions: Consistent with Cohort 1, brexu-cel demonstrated a high ORR, durable responses, and an expected safety profile in pts with R/R MCL in Cohort 2 despite the lower dose. However, small sample size limits interpretation of these results. With >5 y of median follow-up, pts in Cohort 1 and 2 continued to experience durable responses with high 60-mo OS rates. No new safety signals were detected and no secondary malignancies or RCR cases were reported in LTFU. Additionally, ZUMA-2 results are consistent with real-world outcomes of brexu-cel in the post BTKi R/R MCL setting (89% ORR and 81% CR rate; Wang Y, et al. J Clin Oncol. 2023). These results support the continued use of brexu-cel in R/R MCL.

Abstract Background Hypomagnesemia has been correlated with inferior outcomes in patients with large B cell lymphoma (LBCL) undergoing stem cell transplants. As T-cell and myeloid cell dysfunction have been associated with low magnesium conditions, we investigated whether serum magnesium (Mg) levels could predict clinical outcomes in LBCL patients who received chimeric antigen receptor T-cell therapy. Methods Patients with LBCL who received axi-cel under the ZUMA-1 trial or as FDA approved therapy at Mayo Clinic were examined. Serum samples were obtained at specified time points and cytokine analysis was performed. Single cell RNA sequencing was performed on peripheral blood mononuclear cells. The Student T-test, Kruskal Wallis, or Fisher's Exact Tests were used to compare differences in demographics across Mg levels. Survival curves were plotted using the Kaplan-Meier methodology and compared using the Wilcoxon test. Results We found that hypomagnesemia before lymphodepletion chemotherapy predicted for inferior progression-free and overall survival in the pivotal study ZUMA-1 (NCT02348216). These results were validated in an independent cohort of LBCL patients receiving axicabtagene ciloleucel (axi-cel) at Mayo Clinic. Hypomagnesemia correlated with increased inflammatory serum markers and cytokine levels including ferritin, IL-6, IL1Ra, IL-8, and MIP1a. scRNAseq analysis unveiled altered immune interactions between monocytes and T cells with a concordant immune suppressive transcriptome. Conclusions Hypomagnesemia at the time of CAR-T infusion associates with an unfavorable inflammatory profile and decreased response and survival in LBCL patients receiving axi-cel. These findings suggest a potentially actionable prognostic factor for patients with large cell lymphoma undergoing CAR-T.

Background: Axi-cel is a US and EU-approved autologous anti-CD19 chimeric antigen receptor (CAR) T cell therapy for pts with relapsed/refractory large B cell lymphoma after 1 prior therapy as a result of ZUMA-7 (NCT. In ZUMA-1 (NCT02348216), the pivotal study which initially led to the approval of axi-cel in the 3L+ setting, the objective response rate was 83% (58% complete response rate; Locke et al. Lancet Oncol. 2019) and at 5 years follow up an OS rate of 42.6%, 5 years durable response and 5 years disease specific survival at 51% ( Neelapu et al. Blood 2023). T cell-related biology (Immunosign 21; Immunoscore®IC) measured pretreatment in the tumor microenvironment (TME) was associated with response to axi-cel ( Scholler et al., 2022). Increased density of activated PD-1+LAG-3+/−TIM-3−CD8+ T cells, measurable pretreatment, facilitates clinical response in pts post-axi-cel. This expanded analysis characterized the impact of axi-cel treatment on the TME immune contexture and examined associations between immune cell subsets and relapse. Methods: Baseline and post-infusion tumor biopsy samples were analyzed by multiplex immunohistochemistry ( Brightplex®). Four panels were developed and applied to assess T cell infiltration (CD3 CD8 FOXP3 TIM3 PD1 LAG3 TOX), regulatory T cell subtyping (CD3 CD8 GATA3 TBET RORg BCL6), T cell activation & exhaustion (CD3 CD8 TIM3 LAG3 PD1 GZMB KI67), macrophage (CD68 CD64 CD163 CD204 CD206 PDL1) and MDSC (CD3 CD11B CD68 CD14 CD15 LOX1 S100A9) subsets. Transcriptomic analysis was performed using nCounter® Pan Cancer panel. The association between T cell subtypes and macrophages cell subset density, and probability to relapse was evaluated. T test values were based on Brightplex analysis. Results: 34 tumor biopsies (16 at baseline, 18 post-infusion) from 26 pts were analyzed including 11 relapsed (6 CR/5 PR) and 15 durable response (15 CR). The baseline and post-infusion TME comprised all major macrophages, MDSC and T cell subsets, with diverse distribution across samples analyzed. Low proinflammatory M1 macrophage density was observed at baseline and post-infusion across patients. In relapsed patients, baseline tumors were enriched with a significantly higher proportion of protumoral M2 macrophage (p<0.0001). A shift of M1-M2 polarization was observed between baseline and post-infusion (Baseline 33%M1M2 / 65%M2, post infusion 76%M1M2 / 21%M2, p<0,0001) across the cohort. In contrast, in relapsed patients, M-MDSC cell density was significantly increased post treatment (p=0.0420). In addition, Innate lymphocyte cells subtype 2 (ILC2) cell density, previously described to be positively correlated with improved overall survival in CRC ( Huang et al. 2021 Cancers), was significantly decreased in relapsed patients post infusion (p=0.019).Post-infusion, durable response was associated with a significant increase in pan-Macrophages (p=0.0360) and cytotoxic T cell subset densities: CD8 naïve T cells (p=0.016); Activated Cytotoxic T cell (GZMB+)(p=0.0203); PD1+TIM3+LAG3- cytotoxic T cell (p=0.0117); CD8 regulatory T cell (FOXP3+)(p=0.012). Regarding T helper lineage, ongoing response was associated with a significant increase of: CD4 naïve T cells (p=0.021); T helper Th2 (p=0.020); cytotoxic T lymphocyte TC2 and TC1/TC2 cell densities (respectively p=0.0052 and 0.011).Additional characterization of the immune contexture and correlative analysis of cell subsets will be presented. Conclusion: These results suggest that baseline proportions of protumor M2 macrophages may predict disease relapse after axi-cel treatment. Following infusion, relapse is also associated with spatial enrichment of M-MDSC, whereas durable response is related to increases in T cell subpopulation densities inclusive of cytotoxic T cells, T helper, TC1/TC2 ratios and innate T-subpopulations. These findings suggest that axi-cel treatment drastically impacts tumor immune mobilization, infiltration and contexture, which correlates with long term response.

In phase 2 of ZUMA-1, a single-arm, multicenter, registrational trial, axicabtagene ciloleucel (axi-cel) autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy demonstrated durable responses at 2 years in patients with refractory large B-cell lymphoma (LBCL). Here, we aimed to assess survival and safety in ZUMA-1 after 5 years of follow-up. Eligible adults with refractory LBCL (diffuse large B-cell lymphoma, primary mediastinal B-cell lymphoma, and transformed follicular lymphoma) received lymphodepleting chemotherapy followed by axi-cel infusion targeted at 2×106 cells/kg. Investigator-assessed response, updated survival, safety, and pharmacokinetic outcomes were assessed in treated patients. The objective response rate in the 101 treated patients was 83% (58% complete response rate), and with a median follow-up of 63.1 months, responses were ongoing at data cutoff in 31%. Median overall survival (OS) was 25.8 months and the estimated 5-year OS rate was 42.6%. Disease-specific survival (excluding deaths unrelated to disease progression) estimated at 5 years was 51.0%. No new serious adverse events or deaths related to axi-cel were observed after additional follow-up. Peripheral blood B cells were detectable in all evaluable patients at 3 years with polyclonal B-cell recovery in 91%. Ongoing responses at 60 months were associated with early CAR T-cell expansion. In conclusion, this 5-year follow-up analysis of ZUMA-1 demonstrates sustained overall and disease-specific survival, with no new safety signals in patients with refractory LBCL. Protracted B-cell aplasia was not required for durable responses. These findings support the curative potential of axi-cel in a subset of patients with aggressive B-cell lymphomas. ClinicalTrials.gov, number NCT02348216

Abstract Background: Axi-cel, an autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, is approved for the treatment of pts with relapsed/refractory LBCL with ≥ 2 prior systemic therapies. In the 2-year analysis of ZUMA-1 (NCT02348216), the multicenter, single-arm phase 1/2 study evaluating axi-cel in pts with refractory LBCL, the objective response rate (ORR) was 83%, including a complete response (CR) rate of 58%; 39% of pts had ongoing response with a median follow-up of 27.1 months (Locke et al. Lancet Oncol. 2019). EFS is emerging as a robust surrogate endpoint for OS in hematologic malignancies. A recent systematic analysis demonstrated a linear correlation between EFS and OS in pts with diffuse LBCL after first-line immunochemotherapy (Zhu et al. Leukemia. 2020). Here, we report updated survival findings from the phase 2 portion of ZUMA-1 after 4 years of follow-up, including an evaluation of the association of OS with EFS. Methods: Eligible pts had refractory LBCL (diffuse LBCL, primary mediastinal B cell lymphoma, transformed follicular lymphoma). After leukapheresis at enrollment, pts received low-dose conditioning chemotherapy (fludarabine and cyclophosphamide) followed by a target dose of 2×10 6 anti-CD19 CAR T cells/kg (Neelapu et al. N Engl J Med. 2017). The primary endpoint was ORR, with the first response assessment occurring 4 weeks following infusion. Additional endpoints included safety and translational evaluations. An exploratory analysis of OS by EFS at 12 and 24 months was performed. EFS was defined as the time from axi-cel infusion until disease progression, initiation of new lymphoma therapy (excluding stem cell transplant), or death from any cause. Comparisons of OS by EFS outcomes were analyzed via Kaplan-Meier estimates. Results: Of 111 enrolled pts, axi-cel was administered to 101 pts. As of August 11, 2020, median follow-up was 51.1 months. With over 4 years of follow-up, median OS was 25.8 months, and the 4-year OS rate was 44%. Median EFS in pts treated with axi-cel was 5.7 months, with a 12-month EFS rate of 43% (95% CI, 33-52) and a 24-month EFS rate of 38% (95% CI, 28-47). In pts with an EFS event by Month 12 (EFS12; n=57) vs those without EFS12 (n=44), 4-year OS rates were 7% (95% CI, 2-16) vs 91% (95% CI, 78-97), respectively. Among the 17 pts with EFS12 who were alive at Month 12, 13 (76%) died by Month 48, while among the 44 pts alive at Month 12 without EFS12, 4 (9%) died by Month 48. In pts with an EFS event by Month 24 (EFS24; n=62) vs those without EFS24 (n=39), 4-year OS rates were 13% (95% CI, 6-23) vs 92% (95% CI, 78-98), respectively. Among the 12 pts with EFS24 who were alive at Month 24, 4 (33%) died by Month 48, while among the 39 pts alive at Month 24 without EFS24, 3 (8%) died by Month 48. Since the 2-year analysis (Locke et al. Lancet Oncol. 2019), there have been no new safety signals reported, including no new serious adverse events, no axi-cel-related secondary malignancy, and no confirmed cases of replication-competent retrovirus. Overall, 26 pts received subsequent anti-cancer therapy; median time to next therapy was 8.7 months (range, 0.3 - 53.8). Immunoglobulin therapy was administered to 38 (38%) pts. Two pts in axi-cel-induced remission received allogeneic stem cell transplant; 1 pt was in CR and 1 pt was in partial response. Among treated pts, 58 (57%) have died, primarily due to progressive disease (46%; n=46), followed by other reasons (7%; n=7), adverse events (4%; n=4), and secondary malignancy (myelodysplastic syndrome, with onset on Day 574) unrelated to axi-cel (1%; n=1). Among pts without EFS12 and without EFS24, 1 pt each (2% and 3%, respectively) died due to disease progression >24 months following axi-cel infusion; >36 months, 2 pts each (5% for both) died due to disease progression (1 pt each [2% and 3%]) and other reasons (1 pt each [2% and 3%]. One pt (2%) without EFS12 died due to disease progression between 12 and 24 months. Updated findings with ≥5 years of follow-up, including translational correlations, will be presented. Conclusion: In this long-term survival analysis of ZUMA-1 with ≥4 years of follow-up, axi-cel demonstrated longer OS in pts without EFS events at Month 12 and Month 24 vs pts with events at these timepoints. These data support the use of EFS as a surrogate endpoint for long-term OS in refractory LBCL, and the relationship between EFS and 5-year OS will be presented. Disclosures Jacobson: Nkarta: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Kite, a Gilead Company: Consultancy, Honoraria, Other: Travel support; Axis: Speakers Bureau; Pfizer: Consultancy, Honoraria, Other: Travel support, Research Funding; Clinical Care Options: Speakers Bureau; Celgene: Consultancy, Honoraria, Other: Travel support; Precision Biosciences: Consultancy, Honoraria, Other: Travel support; Lonza: Consultancy, Honoraria, Other: Travel support; Novartis Pharmaceuticals Corporation: Consultancy, Honoraria, Other: Travel support; Humanigen: Consultancy, Honoraria, Other: Travel support. Locke: Moffitt Cancer Center: Patents & Royalties: field of cellular immunotherapy; Janssen: Consultancy, Other: Scientific Advisory Role; Gerson Lehrman Group: Consultancy; Novartis: Consultancy, Other, Research Funding; Legend Biotech: Consultancy, Other; Bluebird Bio: Consultancy, Other: Scientific Advisory Role; BMS/Celgene: Consultancy, Other: Scientific Advisory Role; Calibr: Consultancy, Other: Scientific Advisory Role; Cellular Biomedicine Group: Consultancy, Other: Scientific Advisory Role; Iovance Biotherapeutics: Consultancy, Other: Scientific Advisory Role; GammaDelta Therapeutics: Consultancy, Other: Scientific Advisory Role; Emerging Therapy Solutions: Consultancy; Takeda: Consultancy, Other; Wugen: Consultancy, Other; EcoR1: Consultancy; Umoja: Consultancy, Other; Cowen: Consultancy; Kite, a Gilead Company: Consultancy, Other: Scientific Advisory Role, Research Funding; Amgen: Consultancy, Other: Scientific Advisory Role; Allogene Therapeutics: Consultancy, Other: Scientific Advisory Role, Research Funding. Ghobadi: Atara: Consultancy; Amgen: Consultancy, Research Funding; Wugen: Consultancy; Celgene: Consultancy; Kite, a Gilead Company: Consultancy, Honoraria, Research Funding. Miklos: Pharmacyclics, Amgen, Kite, a Gilead Company, Novartis, Roche, Genentech, Becton Dickinson, Isoplexis, Miltenyi, Juno-Celgene-Bristol Myers Squibb, Allogene, Precision Biosciences, Adicet, Adaptive Biotechnologies: Research Funding; Adaptive Biotechnologies, Novartis, Juno/Celgene-BMS, Kite, a Gilead Company, Pharmacyclics-AbbVie, Janssen, Pharmacyclics, AlloGene, Precision Bioscience, Miltenyi Biotech, Adicet, Takeda: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Patents & Royalties; Kite, a Gilead Company, Amgen, Atara, Wugen, Celgene, Novartis, Juno-Celgene-Bristol Myers Squibb, Allogene, Precision Bioscience, Adicet, Pharmacyclics, Janssen, Takeda, Adaptive Biotechnologies and Miltenyi Biotechnologies: Consultancy. Oluwole: Kite, a Gilead Company: Consultancy, Research Funding; Janssen: Consultancy; Pfizer: Consultancy; Curio Science: Consultancy. Lin: Gamida Cell: Consultancy; Legend: Consultancy; Juno: Consultancy; Takeda: Research Funding; Merck: Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy; Bluebird Bio: Consultancy, Research Funding; Vineti: Consultancy; Sorrento: Consultancy; Janssen: Consultancy, Research Funding; Kite, a Gilead Company: Consultancy, Research Funding. Hill: Celgene (BMS): Consultancy, Honoraria, Research Funding; Incyte/Morphysis: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Gentenech: Consultancy, Honoraria, Research Funding; Beigene: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; AstraZenica: Consultancy, Honoraria; Kite, a Gilead Company: Consultancy, Honoraria, Other: Travel Support, Research Funding; Epizyme: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria. Timmerman: Spectrum Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; Bluebird Bio: Current equity holder in publicly-traded company; Marker Therapeutics: Current equity holder in publicly-traded company; Corvus: Current equity holder in publicly-traded company; Genmab: Current equity holder in publicly-traded company; Merck: Research Funding; TG Therapeutics: Current equity holder in publicly-traded company. Deol: Kite, a Gilead Company: Consultancy. Reagan: Seagen: Research Funding; Kite, a Gilead Company: Consultancy; Genentech: Research Funding; Curis: Consultancy. Stiff: Karyopharm: Consultancy, Honoraria; CRISPR Therapeutics: Consultancy, Honoraria; Kite, a Gilead Company: Research Funding; Amgen: Research Funding; Macrogenics: Research Funding; Bristol Myers Squibb: Research Funding; Janssen: Research Funding; Gamida Cell: Research Funding; Seagen: Research Funding; Cellectar: Research Funding; Incyte: Research Funding; BioLineRX: Research Funding; Cellectar: Research Funding; Actinium: Research Funding; MorphoSys: Consultancy, Honoraria. Flinn: Celgene: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; AstraZeneca: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Rhizen Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Loxo: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Agios: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Karyopharm Therapeutics: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Forma Therapeutics: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Infinity Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; ArQule: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Calithera Biosciences: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Yingli Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Verastem: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Unum Therapeutics: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; AbbVie: Consultancy, Other: All Consultancy and Research Funding payments made to Sarah Cannon Research Institute, Research Funding; Kite, a Gilead Company: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Genentech: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; TG Therapeutics: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Roche: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Incyte: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Takeda: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Constellation Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Acerta Pharma: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Novartis: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Gilead Sciences: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Merck: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Seagen: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Portola Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; BeiGene: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Juno Therapeutics: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Janssen: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Nurix Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Pfizer: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Forty Seven: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Curis: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Iksuda Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; IGM Biosciences: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; MorphoSys: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Great Point Partners: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Teva: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Trillium Therapeutics: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Triphase Research & Development Corp.: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Century Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Hutchison MediPharma: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Vincerx Pharma: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Sarah Cannon Research Institute: Current Employment; Servier Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Yingli Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Seagen: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Servier Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Unum Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute, Research Funding; Johnson & Johnson: Current holder of individual stocks in a privately-held company; Seattle Genetics: Research Funding. Farooq: Kite, a Gilead Company: Honoraria. Goy: MorphoSys: Honoraria, Other; Bristol Meyers Squibb: Membership on an entity's Board of Directors or advisory committees; OncLive Peer Exchange: Honoraria; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Acerta: Consultancy, Research Funding; Michael J Hennessey Associates INC: Consultancy; Physicians' Education Resource: Consultancy, Other: Meeting/travel support; Vincerx: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol Meyers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie/Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Honoraria; AstraZeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie/Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Elsevier's Practice Update Oncology, Intellisphere, LLC(Targeted Oncology): Consultancy; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria; Vincerx pharma: Membership on an entity's Board of Directors or advisory committees; Medscape: Consultancy; Xcenda: Consultancy, Honoraria; Janssen: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Genentech/Hoffman la Roche: Research Funding; Infinity/Verastem: Research Funding; Janssen: Research Funding; Rosewell Park: Consultancy; LLC(Targeted Oncology): Consultancy; Hoffman la Roche: Consultancy; Xcenda: Consultancy; Kite, a Gilead Company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Elsevier PracticeUpdate: Oncology: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Genomic Testing Cooperative: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; Karyopharm: Research Funding; Phamacyclics: Research Funding; Constellation: Research Funding; COTA (Cancer Outcome Tracking Analysis): Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; Hackensack Meridian Health, Regional Cancer Care Associates/OMI: Current Employment. Muñoz: Bayer, Kite, a Gilead Company, Celgene, Merck, Portola, Incyte, Genentech, Pharmacyclics, Seagen, and Janssen, Millennium: Research Funding; Kite, a Gilead Company, Kyowa, Bayer, Pharmacyclics, Janssen, Seagen, Acrotech, Aurobindo, Beigene, Verastem, AstraZeneca, Celgene/Bristol Myers Squibb, Genentech, and Roche: Speakers Bureau; Pharmacyclics, Abbvie, Bayer, Kite, a Gilead Company, Pfizer, Janssen, Juno/Celgene, Bristol Myers Squibb, Kyowa, Alexion, Beigene, Fosun Kite, Innovent, Seagen, Debiopharm, Karyopharm, Genmab, ADC Therapeutics, Epizyme, Beigene, and Servier: Consultancy; Targeted Oncology, OncView, Kyowa, Physicians' Education Resource, and Seagen: Honoraria; OncView: Honoraria; Kyowa Kirin: Honoraria; Physicians' Education Resource: Honoraria. Siddiqi: Oncternal: Research Funding; Kite Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Speakers Bureau; AstraZeneca: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BeiGene: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; TG Therapeutics: Research Funding. Shen: Atara: Current Employment, Current equity holder in publicly-traded company, Other: Leadership role, Patents & Royalties; Gilead Sciences: Current equity holder in publicly-traded company; Kite, a Gilead Company: Current Employment, Other: Leadership role, Patents & Royalties. Bot: Kite, a Gilead Company: Current Employment; Gilead Sciences: Consultancy, Current equity holder in publicly-traded company, Other: Travel support. Dong: GliaCure/Tufts: Consultancy, Patents & Royalties; Gilead: Current equity holder in publicly-traded company; Kite, a Gilead Company: Current Employment. Singh: Kite, a Gilead Company: Current Employment. Spooner: Kite, a Gilead Company: Current Employment; Gilead: Current equity holder in publicly-traded company. Karalliyadda: Kite, a Gilead Company: Current Employment; Gilead: Current equity holder in publicly-traded company. Kim: Gilead Sciences: Current equity holder in publicly-traded company; Kite, a Gilead Company: Current Employment. Zheng: Gilead Sciences: Current equity holder in publicly-traded company; Kite, a Gilead Company: Current Employment. Neelapu: Kite, a Gilead Company, Merck, Bristol Myers Squibb, Novartis, Celgene, Pfizer, Allogene Therapeutics, Cell Medica/Kuur, Incyte, Precision Biosciences, Legend Biotech, Adicet Bio, Calibr, Unum Therapeutics and Bluebird Bio: Honoraria; Kite, a Gilead Company, Merck, Bristol Myers Squibb, Novartis, Celgene, Pfizer, Allogene, Kuur, Incyte, Precision BioSciences, Legend, Adicet Bio, Calibr, and Unum Therapeutics: Other: personal fees; Takeda Pharmaceuticals and related to cell therapy: Patents & Royalties; Kite, a Gilead Company, Bristol Myers Squibb, Merck, Poseida, Cellectis, Celgene, Karus Therapeutics, Unum Therapeutics (Cogent Biosciences), Allogene, Precision BioSciences, Acerta and Adicet Bio: Research Funding.

Abstract Background: ZUMA-1 is the registrational Phase 1/2 study of axi-cel, an autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, in pts with refractory LBCL. In ZUMA-1 Cohorts 1+2 (C1+2; N=101), rates of Grade (Gr) ≥3 cytokine release syndrome (CRS) and neurologic events (NEs) were 13% and 28%, respectively, at the 6-mo primary analysis; the objective response rate (ORR) was 82% (54% complete response [CR]; Neelapu et al. NEJM. 2017). ZUMA-1 safety management C6 assessed whether prophylactic and earlier corticosteroids and/or tocilizumab could reduce incidence and severity of CRS and NEs. With a median follow-up of 8.9 mo (N=40) for C6, there were no Gr ≥3 CRS, a low rate of Gr ≥3 NEs (13%), and high response rates (Oluwole et al. BJH. 2021). Here, we present a 1-yr updated analysis of C6 supported by propensity score matching (PSM) analysis to compare outcomes for pts in C6 vs C1+2. Methods: Eligible pts could receive optional bridging therapy after leukapheresis. Pts received conditioning chemotherapy for 3 d prior to a single axi-cel infusion. Pts received once-daily oral dexamethasone 10 mg on Days 0 (before axi-cel), 1, and 2; corticosteroids and/or tocilizumab for adverse event (AE) management were given earlier vs C1+2. The primary endpoints were incidence and severity of CRS and NEs. Other endpoints included efficacy outcomes and biomarker analyses. To ensure comparability for pts in C6 and C1+2, an exploratory PSM analysis was performed after balancing for key baseline disease characteristics (tumor burden, IPI score, no. of prior lines of chemotherapy, disease stage, and LDH level). Results: As of December 16, 2020, the median follow-up time was 14.9 mo. Gr ≥3 AEs were reported in all 40 treated pts, and the most common were neutropenia (45%), neutrophil count decreased (33%), and white blood cell count decreased (23%). No Gr ≥3 CRS occurred. Gr ≥3 NEs were reported in 15% of pts. Median time to CRS and NE onset was 5 and 6 d, respectively, after axi-cel infusion. Infections of any grade occurred in 50% of pts (20% Gr ≥3). Since the 6-mo analysis, no new cases of CRS were observed. Four new axi-cel-related NEs occurred in 2 pts (pt 1: Gr 2 mental status changes and seizure-like phenomena both on Day 441; pt 2: Gr 1 dementia [occurred on Day 93 but was reported late] and Gr 5 toxic encephalopathy on Day 369 [resultant from a Gr 4 event that started on Day 351]). Two new infections of Gr 2 pneumonia and Gr 1 bronchitis were observed; the latter was axi-cel-related. One death due to progressive disease occurred. The investigator-assessed ORR was 95% (80% CR). Median DOR, PFS, and OS were not reached. Kaplan-Meier estimates of the 12-mo DOR, PFS, and OS rates were 60%, 63%, and 82%, respectively. At data cutoff, 53% of pts were in ongoing response. Median peak CAR T-cell levels were comparably high in pts with ongoing response and relapse (64 cells/µL [n=21] and 66 cells/µL [n=15], respectively) at 12 mo and considerably lower in nonresponders (18 cells/µL [n=2]). In all, 32 matched pts each in C6 and C1+2 were identified during PSM analysis; 8 pts from C6 were not included due to nonavailability of matched pts in C1+2. No Gr ≥3 CRS was observed in C6 vs 13% of pts in C1+2. Incidence of Gr ≥3 NEs was comparable in C6 and C1+2 (19% and 22%, respectively), with median time to onset of 12 d in C6 vs 7 d in C1+2. The ORR was 94% in both C6 and matched C1+2 (75% and 78% CR rates, respectively); 47% and 59% of pts were in ongoing response at 12 mo. The Kaplan-Meier estimate of the 12-mo PFS rate was 61% in both C6 and matched C1+2. Median peak CAR T-cell levels were 65 and 43 cells/µL, respectively, in C6 and C1+2. Serum levels of inflammatory biomarkers associated with CAR T-cell treatment-related AEs (IFN-γ, IL-2, GM-CSF, and ferritin) were lower in C6 vs C1+2. Median cumulative corticosteroid dose including prophylaxis was 1252 mg in C6 (n=32) and 7418 mg in C1+2 (n=6). Conclusion: With ≥1-y follow-up, prophylactic and earlier corticosteroid and/or tocilizumab intervention continued to demonstrate a manageable safety profile, absence of new safety signals, and high, durable response rates, which was corroborated by PSM analysis. Although fewer pts in C1+2 received corticosteroids after matching, the median cumulative corticosteroid dose was 4-fold lower in C6 vs C1+2. These findings suggest that the C6 AE management strategy can improve long-term safety of axi-cel in R/R LBCL without compromising durability of responses. Disclosures Oluwole: Pfizer: Consultancy; Curio Science: Consultancy; Janssen: Consultancy; Kite, a Gilead Company: Consultancy, Research Funding. Forcade: Jazz: Other: Travel Support, Speakers Bureau; MSD: Other: Travel Support; Gilead: Other: Travel Support, Speakers Bureau; Novartis: Consultancy, Other: Travel Support, Speakers Bureau. Muñoz: Targeted Oncology: Honoraria; Seagen: Consultancy, Honoraria, Speakers Bureau; Physicians' Education Resource: Honoraria; Kyowa Kirin: Consultancy, Honoraria, Speakers Bureau; OncView: Honoraria; Pharmacyclics: Consultancy, Speakers Bureau; Bayer: Consultancy, Speakers Bureau; Kite, a Gilead Company: Consultancy, Speakers Bureau; Pfizer: Consultancy; Janssen: Consultancy, Speakers Bureau; Juno/Celgene: Consultancy; Bristol Myers Squibb: Consultancy; Alexion: Consultancy; BeiGene: Consultancy, Speakers Bureau; Fosunkite: Consultancy; Innovent: Consultancy; Debiopharma: Consultancy; Karyopharm: Consultancy; Genmab: Consultancy; ADC Therapeutics: Consultancy; Epizyme: Consultancy; Servier: Consultancy; Acrotech: Speakers Bureau; Verastem: Speakers Bureau; AstraZeneca: Speakers Bureau; Celgene/Bristol Myers Squibb: Speakers Bureau; Genentech: Speakers Bureau; Aurobindo: Speakers Bureau. de Guibert: Gilead: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Vose: Kite, a Gilead Company: Honoraria, Research Funding. Bartlett: Roche/Genentech: Consultancy; Seagen: Consultancy, Research Funding; Autolus: Research Funding; Bristol Myers Squibb: Research Funding; Celgene: Research Funding; Forty Seven: Research Funding; Genentech: Research Funding; Janssen: Research Funding; Kite, a Gilead Company: Research Funding; Merck: Research Funding; Millennium: Research Funding; Pharmacyclics: Research Funding; ADC Therapeutics: Consultancy, Research Funding. Lin: Juno: Consultancy; Takeda: Research Funding; Gamida Cell: Consultancy; Vineti: Consultancy; Merck: Research Funding; Sorrento: Consultancy; Legend: Consultancy; Celgene: Consultancy, Research Funding; Novartis: Consultancy; Janssen: Consultancy, Research Funding; Bluebird Bio: Consultancy, Research Funding; Kite, a Gilead Company: Consultancy, Research Funding. Deol: Kite, a Gilead Company: Consultancy. McSweeney: Kite, a Gilead Company: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Research Funding; Autolus: Research Funding; Allovir: Research Funding. Goy: Acerta: Consultancy, Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Xcenda: Consultancy, Honoraria; Vincerx: Honoraria, Membership on an entity's Board of Directors or advisory committees; Elsevier's Practice Update Oncology, Intellisphere, LLC(Targeted Oncology): Consultancy; MorphoSys: Honoraria, Other; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria; Bristol Meyers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie/Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; LLC(Targeted Oncology): Consultancy; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; OncLive Peer Exchange: Honoraria; Rosewell Park: Consultancy; Genomic Testing Cooperative: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; COTA (Cancer Outcome Tracking Analysis): Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; Celgene: Consultancy, Honoraria, Research Funding; Xcenda: Consultancy; Gilead: Membership on an entity's Board of Directors or advisory committees; Michael J Hennessey Associates INC: Consultancy; Bristol Meyers Squibb: Membership on an entity's Board of Directors or advisory committees; Medscape: Consultancy; AbbVie/Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Hoffman la Roche: Consultancy; Infinity/Verastem: Research Funding; Genentech/Hoffman la Roche: Research Funding; Physicians' Education Resource: Consultancy, Other: Meeting/travel support; Janssen: Membership on an entity's Board of Directors or advisory committees; Vincerx pharma: Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria; AstraZeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kite, a Gilead Company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Elsevier PracticeUpdate: Oncology: Consultancy, Honoraria; Janssen: Research Funding; Karyopharm: Research Funding; Phamacyclics: Research Funding; Constellation: Research Funding; Hackensack Meridian Health, Regional Cancer Care Associates/OMI: Current Employment. Kersten: Miltenyi Biotec: Consultancy, Honoraria, Other: Travel support; Roche: Consultancy, Honoraria, Other: Travel support, Research Funding; BMS/Celgene: Consultancy, Honoraria; Takeda: Research Funding; Celgene: Research Funding; Kite, a Gilead Company: Consultancy, Honoraria, Other: Travel support, Research Funding; Novartis: Consultancy, Honoraria, Other: Travel support. Jacobson: Nkarta: Consultancy, Honoraria; Novartis Pharmaceuticals Corporation: Consultancy, Honoraria, Other: Travel support; Humanigen: Consultancy, Honoraria, Other: Travel support; Lonza: Consultancy, Honoraria, Other: Travel support; AbbVie: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria, Other: Travel support, Research Funding; Precision Biosciences: Consultancy, Honoraria, Other: Travel support; Kite, a Gilead Company: Consultancy, Honoraria, Other: Travel support; Celgene: Consultancy, Honoraria, Other: Travel support; Axis: Speakers Bureau; Clinical Care Options: Speakers Bureau. Farooq: Kite, a Gilead Company: Honoraria. Minnema: Cilag: Consultancy; BMS: Consultancy; Janssen: Consultancy; Celgene: Other: Travel expenses; Kite/Gilead: Consultancy; Alnylam: Consultancy. Thieblemont: Bristol Myers Squibb/Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Kyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses , Research Funding; Gilead Sciences: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Cellectis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses ; Hospira: Research Funding; Bayer: Honoraria; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses . Timmerman: Spectrum Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; Bluebird Bio: Current equity holder in publicly-traded company; TG Therapeutics: Current equity holder in publicly-traded company; Marker Therapeutics: Current equity holder in publicly-traded company; Corvus: Current equity holder in publicly-traded company; Genmab: Current equity holder in publicly-traded company; Merck: Research Funding. Stiff: Macrogenics: Research Funding; Amgen: Research Funding; Kite, a Gilead Company: Research Funding; Seagen: Research Funding; Gamida Cell: Research Funding; Janssen: Research Funding; CRISPR Therapeutics: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Cellectar: Research Funding; Bristol Myers Squibb: Research Funding; Incyte: Research Funding; BioLineRX: Research Funding; Cellectar: Research Funding; MorphoSys: Consultancy, Honoraria; Actinium: Research Funding. Avivi: Novartis: Speakers Bureau; Kite, a Gilead Company: Speakers Bureau. Tzachanis: Fate Therapeutics: Research Funding; Incyte: Research Funding; Genentech: Research Funding; Bristol Myers Squibb: Research Funding; Magenta: Consultancy; Kyowa Kirin: Consultancy; Kite, a Gilead Company: Consultancy, Research Funding, Speakers Bureau; EUSA: Consultancy; Takeda: Consultancy, Speakers Bureau; Partner: Consultancy. Kim: Kite, a Gilead Company: Current Employment; Gilead Sciences: Current equity holder in publicly-traded company. Zheng: Kite, a Gilead Company: Current Employment; Gilead Sciences: Current equity holder in publicly-traded company. Shen: Gilead Sciences: Current equity holder in publicly-traded company; Atara: Current Employment, Current equity holder in publicly-traded company, Other: Leadership role, Patents & Royalties; Kite, a Gilead Company: Current Employment, Other: Leadership role, Patents & Royalties. Vardhanabhuti: Kite, a Gilead Company: Current Employment, Other: Travel support, Research Funding; Gilead Sciences: Current equity holder in publicly-traded company. Van Meerten: Kite, a Gilead Company: Honoraria; Janssen: Consultancy.

Abstract Introduction:Pathogenic and/or founder germline variants in the ataxia-telangiectasia mutated (ATM) gene confer an increased breast cancer (BC) risk. The protein kinase ATM plays a central role inDNA double-strand break-repair and in the activation of downstream targets such as p53 and BRCA1. We sought to define the repertoire of somatic genetic alterations of BCs from patients with pathogenic germline ATM mutations and whether somatic loss of heterozygosity (LOH) of ATM would be present in these cancers. Methods: 21 BCs from ATM germline mutation carriers were microdissected. Tumor and normal DNA samples were subjected to whole-exome sequencing (WES, n=12) or massively parallel sequencing targeting all coding regions and selected intronic and regulatory regions of 410 key cancer genes (n=9). Somatic mutations, copy number alterations, cancer cell fractions, large-scale state transitions (LSTs) and mutational signatures were defined using state-of-the-art bioinformatics algorithms. ABSOLUTE and FACETS were employed to assess LOH of the wild-type allele of ATM. Results: Of the patients included in this study, 71%, 24% and 5% of cases harbored ATM missense (all but one p.V2424G), frame-shift and nonsense germline mutations, respectively. All tumors were ER-positive and four (19%) were HER2-positive. The median age of the patients was 46 years (32–79 years). Our analyses revealed biallelic inactivation of ATM through LOH of the wild-type allele in 16 of 21 cases (76%), and second somatic ATM mutations were not found. The median number of non-synonymous somatic mutations was 38 (range 15-113) and 2 (range 0-8)in tumors subjected to WES and targeted sequencing, respectively. The repertoire of somatic genetic alterations of ATM-associated BCs was found to be heterogeneous, including clonal PIK3CA mutations (24%), GATA3 mutations (19%), FANCI amplifications (19%) and CCND1 amplifications (14%). Importantly, however, no somatic mutations affecting TP53 were found. Analysis of the WES data revealed that 5 (42%) ATM-associated BCs displayed high LST scores, all of which harbored bi-allelic ATM inactivation. In contrast to BRCA1- and BRCA2-associated BCs, which frequently display the mutational signature 3 associated with defective homologous recombination DNA repair, the ATM-associated BCs studied displayed the ageing mutational signature (i.e. signature 1). Comparison of the mutational profiles of the ATM--associated BCs subjected to WES (n=12) with those of BRCA1- (n=11) and BRCA2-associated (n=10) BCs from The Cancer Genome Atlas revealed that TP53 was more frequently mutated in BCs from BRCA1 germline mutation carriers (0% vs 72%, P<0.001), while no differences with BRCA2-associated BCs were found. Conclusion: ATM-associated BCs frequently display bi-allelic ATM inactivation through LOH of the wild-type allele and a subset of these cases displayed high levels of LSTs. These findings suggest that at least in a subset of ATM-associated BCs, biallelic inactivation of ATM rather than a dominant negative effect of the germline mutation may be the mechanism of inactivation of this tumor suppressor gene. The repertoire of somatic genetic alterations of ATM-associated BCs is heterogeneous, with a noticeable lack of TP53 somatic mutations. Citation Format: Weigelt B, Bi R, Kumar R, James PA, Thorne H, Couch FJ, Eccles DM, Blows F, Geyer FC, Li A, Selenica P, Lim RS, Blecua P, Shen R, Wen H, Robson ME, Reis-Filho JS, Chenevix-Trench G. The landscape of somatic genetic alterations in breast cancers from ATM germline mutation carriers [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD1-15.