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TPS10066 Background: The SMARCB1/A4 gene products are core subunits of the SWItch/Sucrose Non-fermentable (SWI/SNF) chromatin remodeling complex. Tumors with defects in SWI/SNF are histologically distinct aggressive cancers occurring in children and young adults. SMARCB1/A4 deficient tumors, particularly rhabdoid tumors, poorly differentiated chordoma, epithelioid sarcoma, and medullary renal cell carcinoma, have immune cell infiltrates and programmed death ligand 1 (PD-L1) expression. Response to immune checkpoint inhibition (CI) has been observed in SMARCB1/A4 deficient tumors; however, responses are not durable. T cell immunoreceptor with Ig and ITIM domains (TIGIT) is a novel inhibitory receptor expressed on multiple immune cells. TIGIT inhibits T and NK cells by binding to its ligand poliovirus receptor (PVR) and Nectin2 on tumor cells and antigen-presenting cells. Utilizing RNAseq data, SMARCB1/A4 deficient tumors demonstrate high expression of PVR and Nectin2. Tiragolumab is an antibody to the TIGIT receptor. In patients with non-small cell lung cancer, tiragolumab with atezolizumab increased survival compared to atezolizumab alone. Thus, data suggest that SMARCB1/A4 deficient tumors are susceptible to CI; however, monotherapy is unlikely to achieve durable responses; the addition of tiragolumab may enhance response rates. Methods: This is a phase 1/2 trial of tiragolumab monotherapy and in combination with atezolizumab in patients ≥ 12 months of age with SMARCB1/A4 deficient tumors administered IV on Day 1 of 21-day cycles. Part A will evaluate the safety of tiragolumab monotherapy (300 mg if ≤ 15 kg; 420 mg if >15 to ≤ 40 kg; 600 mg if > 40 kg or ≥ 18 yrs) based on cycle 1 DLTs in up to 6 evaluable patients <18 yrs of age. Part B will estimate the antitumor activity of tiragolumab in combination with atezolizumab (15 mg/kg [max 1200 mg]) if < 18 yrs or 1200 mg if ≥ 18 yrs) in 6 histology-specific cohorts (renal medullary carcinoma, malignant rhabdoid tumor, atypical teratoid rhabdoid tumor, poorly differentiated carcinoma, epithelioid sarcoma, and other) Each cohort will be conducted using a 6+4 Simon’s two stage design. Up to 13 patients may enroll in each cohort allowing for inevaluable patients (maximum n=78). Enrollment of patients ≥ 18 yrs on Part B may occur concurrently with enrollment of patients < 18 yrs on Part A. If the pediatric dose of tiragolumab is deemed safe, patients <18 yrs old may be enrolled on Part B. Cycle 1 toxicities of the combination therapy will be monitored in Part B using a Bayesian Optimal Interval Design in patients < 12 yrs of age. The secondary objectives are to characterize pharmacokinetics/anti-drug antibody and estimating progression free survival, overall survival, and duration of response. Enrollment is open for all Pediatric Early Phase Clinical Trial Network sites. Clinical trial information: NCT05286801 .

PURPOSE Compared with people living without HIV (PWOH), people living with HIV (PWH) and cancer have traditionally been excluded from immune checkpoint inhibitor (ICI) trials. Furthermore, there is a paucity of real-world data on the use of ICIs in PWH and cancer. METHODS This retrospective study included PWH treated with anti–PD-1- or anti–PD-L1-based therapies for advanced cancers. Kaplan-Meier method was used to estimate overall survival (OS) and progression-free survival (PFS). Objective response rates (ORRs) were measured per RECIST 1.1 or other tumor-specific criteria, whenever feasible. Restricted mean survival time (RMST) was used to compare OS and PFS between matched PWH and PWOH with metastatic NSCLC (mNSCLC). RESULTS Among 390 PWH, median age was 58 years, 85% (n = 331) were males, 36% (n = 138) were Black; 70% (n = 274) received anti–PD-1/anti–PD-L1 monotherapy. Most common cancers were NSCLC (28%, n = 111), hepatocellular carcinoma ([HCC]; 11%, n = 44), and head and neck squamous cell carcinoma (HNSCC; 10%, n = 39). Seventy percent (152/216) had CD4+ T cell counts ≥200 cells/µL, and 94% (179/190) had HIV viral load <400 copies/mL. Twenty percent (79/390) had any grade immune-related adverse events (irAEs) and 7.7% (30/390) had grade ≥3 irAEs. ORRs were 69% (nonmelanoma skin cancer), 31% (NSCLC), 16% (HCC), and 11% (HNSCC). In the matched mNSCLC cohort (61 PWH v 110 PWOH), 20% (12/61) PWH and 22% (24/110) PWOH had irAEs. Adjusted 42-month RMST difference was –0.06 months (95% CI, –5.49 to 5.37; P = .98) for PFS and 2.23 months (95% CI, –4.02 to 8.48; P = .48) for OS. CONCLUSION Among PWH, ICIs demonstrated differential activity across cancer types with no excess toxicity. Safety and activity of ICIs were similar between matched cohorts of PWH and PWOH with mNSCLC.

506 Background: Despite response to systemic therapy, few metastatic urothelial carcinoma (mUC) patients (pts) achieve durable responses. Mutations in the COMPASS-related proteins KMT2D, KMT2C, and KDM6A are found in 66% of UC patients suggesting histone regulation may be an acquired mechanism of tumor viability. We previously found regression of UC in mice when treated with EZH2 inhibitor, tazemetostat. In vivo administration of tazemtostat enhanced the immune response with direct regulation of cytokines and antigen recognition machinery (MHCI and MHCII). We hypothesized that restoration of epigenetic imbalance, combined with immunotherapy, may improve outcomes in mUC pts. Methods: ETCTN 10183 (NCT03854474) is a pilot study evaluating the efficacy of tazemetostat 800 mg BID + pembrolizumab 200 mg every 3 weeks for cisplatin-refractory (Cohort A) or cisplatin/chemo-ineligible advanced UC (Cohort B) pts, with N=12 pts in each cohort. The primary objective is to identify the recommended phase two dose (RP2D) of tazemetostat in combination with pembrolizumab. Secondary objectives include RECIST-based response rate, safety, and progression-free survival. The maximum planned treatment duration is 2 years. Translational objectives include defining total and COMPASS-related genes tumor mutational burden, tumor subtyping, TCR clonality, T cell infiltration, and PDL-1 expression. Results: In the safety lead-in phase, 6 mUC pts were treated. There were no dose-limiting toxicities (DLTs). The RP2D for tazemetostat was established at 800 mg BID. Here we report results of fully accrued cohort A (N=12); 67% males, 33% females, 83% white, 8.3% Black, and 25% Hispanic/Latino ethnicity. The primary sites of UC were: bladder (n=9, 75%), renal pelvis (n=2, 17%), and ureter (n=1, 8.3%). The median (interquartile range, IQR) time since primary diagnosis was 1.1 years (0.7, 1.9); 11/12 patients had non-nodal metastatic disease; 10/12 had 1 or more visceral/bone metastasis. Median number of treatment cycles was 5 (IQR: 3-11; range 1-35). Median duration on protocol treatment was 12 weeks (IQR: 7-30; range 3-107 weeks). Three pts had treatment related grade 3/4 AEs: grade 4 sepsis (n=1), grade 3 lymphopenia (n=2); anemia, increased alkaline-phosphatase, and HSV oral infection (n=1 each). Best response was partial response (PR) in 3 pts (25%) and 3 (25%) had stable disease. Median PFS was 3.1 months (95%CI: 2.3-NA), and median overall survival was 8.0 months (95% CI: 4.7 – NA). Conclusions: The RP2D dose for tazemetostat is 800 mg + 200 mg Pembrolizumab q 3 weeks. The combination was feasible, well tolerated, and resulted in durable responses in poor-risk chemo-refractory UC patients. Clinical trial information: 03854474 .

Abstract Novel treatment strategies are needed for the treatment of Philadelphia chromosome–positive (Ph+) acute lymphoblastic leukemia (ALL) in older patients. This trial evaluated the feasibility and outcomes with the anti-CD19 bispecific T-cell–engaging antibody, blinatumomab, in combination with dasatinib and steroids. Patients 65 years of age or older with Ph+ or Ph-like ALL (with dasatinib-sensitive fusions/mutations) were eligible and could be newly diagnosed or relapsed/refractory. Induction therapy consisted of dasatinib/prednisone. Patients not achieving response by day 56 proceeded to blinatumomab reinduction therapy. Patients achieving response with induction or reinduction therapy proceeded to blinatumomab/dasatinib postremission therapy for 3 cycles followed by dasatinib/prednisone maintenance. All patients received central nervous system prophylaxis with intrathecal methotrexate for a total of 8 doses. Response was assessed at days 28, 56, and 84 and at additional time points based on response parameters. Measurable residual disease was assessed centrally by 8-color flow cytometry at day 28. A total of 24 eligible patients with newly diagnosed Ph+ ALL were enrolled with a median age of 73 years (range, 65-87 years). This combination was safe and feasible. With a median of 2.7 years of follow-up, 3-year overall survival and disease-free survival were 87% (95% confidence interval [CI], 64-96) and 77% (95% CI, 54-90), respectively. Although longer follow-up is needed, these results are encouraging, and future trials are building on this backbone regimen. This trial was registered at www.clinicaltrials.gov as #NCT02143414.

LBA7564 Background: Patients with r/r B-NHL have a dismal prognosis. DIAL (Dual Immunomodulation in Aggressive Lymphoma) was a multi-center randomized phase II study testing the efficacy of nivolumab (PD-1 inhibitor) plus varlilumab (CD27 agonist) in this population. Methods: Patients were randomized (1:1) to nivolumab (240 mg IV every 2 weeks for 4 months, 480 mg IV monthly thereafter; group 1) alone or combined with varlilumab (3 mg/kg IV monthly; group 2). Cross-over (group 1 to 2) was allowed for progression. Primary endpoint was overall response (ORR) per LYRIC criteria. A sample size of 48 patients per arm would provide 80% power to detect increase in ORR from 25% to 45% using a one-sided test (p = 0.15). Pre-specified interim analysis occurred after half of the patients completed first radiologic assessment. Secondary endpoints included overall survival (OS), progression-free survival (PFS), and adverse events (AEs). Exploratory endpoints included tumor genomic assessment and immune profiling of blood and tumor. Results: 53 patients were enrolled (27 in group 1; 26 in group 2). Interim analysis included 24 patients from each arm. Mean age was 65.2 years, 34 (70.8%) were male, and 36 (75%) received prior CAR-T cell therapy. Baseline characteristics were balanced between arms. Grade ≥ 3 AEs were observed in 8 (33.3%) and 7 (30.4%) of patients in groups 1 and 2, respectively. Common AEs (> 5%) of any grade included fatigue, lymphopenia, diarrhea, rash. There were no treatment-associated deaths. Toxicity profile was similar between arms. Table summarizes efficacy outcomes. ORR was achieved in 6 patients (12.5%), not statistically different between arms; 4 responses were complete. Seven patients crossed over (1 responded after crossing). Median OS (8.6 vs 7.3 months; p = 0.39) and PFS (2.7 vs 1.4 months; p = 0.06) were similar between arms. Subgroup analysis of patients with prior CAR-T cell therapy showed similar ORR (5/36; 14%), not statistically different between arms. Correlative analysis results will be presented at conference. The trial met futility criterion on interim analysis and enrollment ceased based on pre-specified stopping rule. Conclusions: Dual immunomodulatory therapy did not enhance anti-tumor activity in patients with aggressive B-NHL compared to nivolumab alone. Response rates were low and consistent with previous data using PD-1 inhibitors in this population. Prior therapy with CAR-T cell does not seem to sensitize patients to PD-1 blockade. Toxicity profile was acceptable and dual therapy did not increase the rate of AEs. Clinical trial information: NCT03038672. [Table: see text]

PURPOSE Chemotherapy outcomes in older patients with Philadelphia (Ph) chromosome–negative B-acute lymphoblastic leukemia (ALL) are very poor. Here, we evaluated blinatumomab as induction and consolidation therapy followed by prednisone, vincristine, 6-mercaptopurine, and methotrexate (POMP) maintenance chemotherapy in this patient population. PATIENTS AND METHODS Patients were treated at National Clinical Trial Network sites. Eligibility criteria included age ≥ 65 years and newly diagnosed Ph chromosome–negative B-ALL. Patients received blinatumomab as induction for one-two cycles until attainment of response (complete remission (CR) and CR with incomplete count recovery). Patients then received three cycles of consolidation with blinatumomab followed by 18 months of POMP maintenance chemotherapy. Eight doses of intrathecal methotrexate were administered as central nervous system prophylaxis. RESULTS Twenty-nine eligible patients were enrolled. The median age was 75 years, and the median bone marrow blast count at diagnosis was 87%. Cytogenetic risk was poor in 10 patients (34%), and five of 14 patients (36%) tested had the Ph-like ALL gene signature. Nineteen patients (66%; 95% CI, 46 to 82) achieved CR. Kaplan-Meier 3-year disease-free survival and overall survival estimates were 37% (95% CI, 17 to 57) and 37% (95% CI, 20 to 55), respectively. CONCLUSION Blinatumomab was well tolerated and effective in the treatment of older patients with newly diagnosed Ph chromosome–negative B-ALL, including patients with poor-risk cytogenetics. The 3-year disease-free survival and overall survival results are encouraging and suggest that this approach should be further explored.

Abstract Tyrosine kinase inhibitors (TKIs) have improved the outcomes of patients with Philadelphia chromosome positive (Ph+) acute lymphoblastic leukemia (ALL). Many older patients (pts) are not good candidates for intensive chemotherapy and are treated with TKIs plus corticosteroids or low intensity chemotherapy. Although the remission rates with this approach have been high, the median disease-free survival (DFS) has been short. Therefore, novel treatment strategies are needed. This trial evaluated the feasibility of combining the TKI dasatinib with prednisone and blinatumomab in older pts with Ph+ ALL. Methods: This trial was activated through the NCTN in January 2015 and closed to accrual in April 2021. Pt eligibility included: age ≥ 65 years; Ph+ or Ph-like ALL (with dasatinib-sensitive fusions or mutations); newly diagnosed or relapsed/ refractory; no evidence of central nervous system (CNS) disease; and adequate organ function. Treatment: For induction, pts received dasatinib 140 mg/d orally (PO) Days 1-56 along with prednisone 60 mg/m 2/d PO Days 1-24. Pts achieving complete remission (CR) or CR with incomplete count recovery (CRi) (Day 28 or Day 56) continued dasatinib until Day 84 followed by 3 cycles of post-remission therapy (PRT) with blinatumomab/ dasatinib. Pts not achieving CR or CRi by Day 56 received re-induction with blinatumomab. Response was assessed at Day 35 of blinatumomab. Pts not achieving CR/ CRi could receive a second cycle of blinatumomab. This was followed by 3 cycles of PRT with blinatumomab/ dasatinib. Maintenance therapy consisted of prednisone 60 mg/m 2/d x 5 days every 28 days for a total of 18 cycles along with dasatinib 140 mg po qd indefinitely. CNS prophylaxis included intrathecal (IT) methotrexate every 4-6 weeks x 8 doses. IT methotrexate was given at least 2 days apart from blinatumomab. Response was assessed at Days 28, 56, 84 and additional time points were dependent on response. Minimal residual disease (MRD) was assessed centrally by multi-color flow cytometry at Day 28. Statistics: 9 eligible/ evaluable pts receiving PRT were to be evaluated before enrolling additional pts. Dose-limiting toxicities (DLTs) were defined as: &gt; Grade 3 non-hematologic toxicities with the exception of nausea, vomiting, or diarrhea (if manageable with supportive care measures) or Grade 4 neutropenia lasting &gt; 42 days with possible relationship to dasatinib or blinatumomab. If due to unexpected accrual, 12 pts were evaluable for DLT, the following rules would apply. If &gt; 4 of the 12 pts experienced a DLT, the study would be temporarily closed pending review. Upon re-opening, 8 additional eligible and evaluable pts would be enrolled for a total of 20 pts receiving blinatumomab. Results: Due to rapid accrual, 16 pts enrolled before accrual was paused to assess feasibility and safety. Twelve pts were evaluable for DLT and 4 experienced a DLT: Grade 3 dyspnea and gastrointestinal pain (n=1), Grade 3 hypertension (n=1), Grade 3 dyspnea (n=1), Grade 3 hyperglycemia (n=1). These adverse events were deemed acceptable by the NCI and FDA and the study re-opened. A total of 25 eligible pts were accrued. The median age was 73 years (range 62-87). All pts were newly diagnosed. One pt was Ph-like, with the remainder being Ph+; 89% of Ph+ pts had additional cytogenetic abnormalities. During induction, 2 pts experienced treatment-related non-hematologic Grade 4 toxicities. No Grade 4 or higher treatment-related non-hematologic toxicities occurred during post-remission therapy or maintenance. Twenty-three out of 25 pts (92%) achieved a CR during dasatinib-based and prednisone induction therapy. Four did not receive PRT (2 due to adverse events, 1 to receive transplant, 1 because of insurance issues). Sixteen pts who achieved CR had MRD data. Five out of 16 pts (31%) were MRD negative at Day 28. One pt remains on PRT and 10 are on maintenance. The median follow up for pts who are alive is 1.7 years. The median overall survival (OS) and DFS have not been reached as of July 8, 2021. Kaplan-Meier 3-year estimates of OS and DFS are 85% (95% CI 58%-95%) and 80% (95% CI 55%-92%), respectively (Figure). Conclusions: This trial demonstrates the feasibility of combining dasatinib and blinatumomab in Ph+ ALL. In addition, with 1.7 years of follow up, outcomes are encouraging with high estimated 3-year DFS and OS. Longer follow up will be needed to determine the durability of these results. Figure 1 Figure 1. Disclosures Advani: Kite Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Research Funding; Glycomimetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Immunogen: Research Funding; OBI: Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Research Funding; Macrogenics: Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Moseley: BioSight Ltd: Consultancy. Wood: Pfizer, Amgen, Seattle Genetics: Honoraria; Juno, Pfizer, Amgen, Seattle Genetics: Other: Laboratory Services Agreement. Park: Intellia: Consultancy; Kura Oncology: Consultancy; BMS: Consultancy; Affyimmune: Consultancy; Curocel: Consultancy; Novartis: Consultancy; Artiva: Consultancy; PrecisionBio: Consultancy; Servier: Consultancy; Kite Pharma: Consultancy; Innate Pharma: Consultancy; Minerva: Consultancy; Autolus: Consultancy; Amgen: Consultancy. Wieduwilt: Gilead: Membership on an entity's Board of Directors or advisory committees; Reata: Current holder of stock options in a privately-held company. Jeyakumar: Jazz: Research Funding; Pfizer: Research Funding. Atallah: Abbvie: Consultancy, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Takeda: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Amgen: Consultancy. Gerds: PharmaEssentia Corporation: Consultancy; CTI BioPharma: Research Funding; Sierra Oncology: Consultancy; AbbVie: Consultancy; Celgene/Bristol Myers Squibb: Consultancy; Constellation: Consultancy; Novartis: Consultancy. O'Brien: Amgen, Astellas, Celgene, GlaxoSmithKline, Janssen Oncology, Aptose Biosciences Inc., Vaniam Group LLC, AbbVie, Alexion, Verastem, Juno Therapeutics, Vida Ventures, Autolus, Johnson and Johnson, Merck, Bristol Myers Squibb, NOVA Research Company, Eli Lill: Consultancy; Kite, Regeneron, Acerta, Caribou, Gilead, Pharmacyclics, TG Therapeutics, Pfizer, Sunesis: Research Funding. Othus: Celgene: Other: Data safety monitoring board; Merck: Consultancy; Biosight: Consultancy; Glycomimetics: Other: Data safety monitoring board; Daiichi Sankyo: Consultancy. Litzow: Jazz: Other: Advisory Board; Pluristem: Research Funding; Amgen: Research Funding; Actinium: Research Funding; Omeros: Other: Advisory Board; Astellas: Research Funding; AbbVie: Research Funding; Biosight: Other: Data monitoring committee. Stone: Actinium: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Arog: Consultancy, Research Funding; Astellas: Membership on an entity's Board of Directors or advisory committees; BerGen Bio: Membership on an entity's Board of Directors or advisory committees; Boston Pharmaceuticals: Consultancy; Bristol Myers Squibb: Consultancy; Elevate Bio: Membership on an entity's Board of Directors or advisory committees; Foghorn Therapeutics: Consultancy; Gemoab: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy; Innate: Consultancy; Janssen: Consultancy; Jazz: Consultancy; Novartis: Consultancy, Research Funding; Onconova: Consultancy; Syndax: Membership on an entity's Board of Directors or advisory committees; Syntrix/ACI: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Aprea: Consultancy; Amgen: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; Agios: Consultancy, Research Funding; Celgene: Consultancy; Macrogenics: Consultancy. Erba: AbbVie Inc; Agios Pharmaceuticals Inc; ALX Oncology; Amgen Inc; Daiichi Sankyo Inc; FORMA Therapeutics; Forty Seven Inc; Gilead Sciences Inc; GlycoMimetics Inc; ImmunoGen Inc; Jazz Pharmaceuticals Inc; MacroGenics Inc; Novartis; PTC Therapeutics: Research Funding; AbbVie Inc; Agios Pharmaceuticals Inc; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Incyte Corporation; Jazz Pharmaceuticals Inc; Novartis: Speakers Bureau; AbbVie Inc: Other: Independent review committee; AbbVie Inc; Agios Pharmaceuticals Inc; Astellas; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Daiichi Sankyo Inc; Genentech, a member of the Roche Group; GlycoMimetics Inc; Incyte Corporation; Jazz Pharmaceuticals Inc; Kura Oncology; Nov: Other: Advisory Committee.

Abstract Background: CML is managed by life-long TKI therapy in most pts which can be associated with chronic toxicities and substantial costs. Discontinuation of TKI in some pts can result in sustained therapy-free remission (TFR); however only a minority are candidates for discontinuation approaches; of those most still relapse and must restart TKI. High expression of programmed death receptor-1 (PD-1) and its ligand PD-L1 on CML-specific cytotoxic T-cells and CML cells, respectively, suggests that PD-1/PD-L1-mediated immune escape contribute to CML persistence and relapse after TKI discontinuation. We designed the BLAST MRD CML trial (NCT#03516279) to study whether adding anti-PD-1 antibody pembrolizumab to TKI therapy is safe and tolerable and increases rate of conversion to undetectable minimal residual disease (UMRD). We present data from the early safety cohort from this ongoing trial with a data cut-off date June 15th, 2021. Methods: BLAST MRD CML-1 is an ongoing national, ECOG-sponsored, single-arm pilot phase II clinical trial that enrolls adults with chronic phase CML who achieved a major molecular response (MR 3) but not UMRD while on a stable dose of up to three lines of TKI therapy. UMRD was defined as an undetectable BCR-ABL by central RQ-PCR (assay sensitivity of 4.5 [MR 4.5]) on 2 consecutive samples separated by ≥4 weeks. Once enrolled, pts continue on TKI and concurrently receive pembrolizumab 200mg IV on day (D)1 of each 21-D cycle with central MRD assessment every 4 cycles for 17 cycles. Pts who achieve UMRD at or prior to C17 discontinue pembrolizumab, while those with persistent MRD continue TKI + pembrolizumab for another 18 cycles. TKI is discontinued one year following first documentation of UMRD. After TKI discontinuation, BCR-ABL is monitored at defined intervals for 24 months. Primary endpoint is proportion of CML pts on stable-dose TKI who convert to UMRD within 2 years (yrs) of combined TKI + pembrolizumab therapy. Secondary endpoints include rates of TKI discontinuation and proportion of pts achieving 2-year TFR, MRD kinetics, and safety. Immune related and other adverse events (AE) were assessed and graded according to CTCAE v 5.0. Results: As of cut-off date, 6 pts enrolled in safety cohort. Median age was 43 yrs (range 32-65). TKIs received on trial included imatinib (N=2), dasatinib (N=3), and nilotinib (N=1). All 6 pts were on 2 nd line TKI. Median exposure to pembrolizumab was 20 doses (range, 5-36). Five pts were still on combined pembrolizumab + TKI treatment, while the 6 th pt has completed combined therapy for 2 yrs and then continued TKI monotherapy on trial after achievement of UMRD (pt has to be in UMRD for 1 yr before TKI can be discontinued). The combination of TKI and pembrolizumab was safe and well tolerated (Table 1). Only 3 pts experienced grade (G) 1/2 AEs as the worst non-hematologic AE while on trial. Hematologic toxicity reported was also generally minimal with only one G 1/2 anemia AE. The only reported G3 AE was a lipase elevation (283 U/L, normal range 11 - 55 U/L) noted on routine laboratory assessment in a pt receiving nilotinib at 400mg BID dose after 48 weeks of starting on trial combined therapy. Amylase was also elevated at G2. No baseline lipase levels were available as protocol at that time did not require baseline assessments. The pt had no symptoms and CT imaging showed no radiologic evidence of pancreatitis. The lipase and amylase levels normalized with holding of both nilotinib and pembrolizumab for 7 weeks, and the AE did not recur with resumption of combined therapy at same dose of pembrolizumab but with nilotinib reduced to 400mg daily. No G4 or 5 AEs occurred. No other dose-adjustments or treatment discontinuation/interruptions due to AEs occurred. No immune-related AEs (IRAEs) have been reported. Discussion: Data from the early safety cohort suggest that the combination of TKI and pembrolizumab is safe and well tolerated. The AEs observed were mild and generally G1/2. No pt discontinued trial therapy due to AEs. Only one G3 AE (asymptomatic lipase elevation) was reported, which could have been related to nilotinib therapy and could have predated trial entry as no baseline lipase value was available and was fully reversible with a temporary hold of therapy. No IRAEs have been reported to date. Work is ongoing on an amendment to study protocol to enhance accrual. Efficacy results will be reported as they mature. Figure 1 Figure 1. Disclosures Zeidan: Boehringer Ingelheim: Consultancy, Research Funding; Ionis: Consultancy; Gilead: Consultancy, Other: Clinical Trial Committees; Loxo Oncology: Consultancy, Other: Clinical Trial Committees; Daiichi Sankyo: Consultancy; Incyte: Consultancy, Research Funding; Astex: Research Funding; Jasper: Consultancy; Cardiff Oncology: Consultancy, Other: Travel support, Research Funding; Aprea: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; BeyondSpring: Consultancy; BMS: Consultancy, Other: Clinical Trial Committees, Research Funding; Acceleron: Consultancy, Research Funding; Novartis: Consultancy, Other: Clinical Trial Committees, Travel support, Research Funding; Genentech: Consultancy; Epizyme: Consultancy; AstraZeneca: Consultancy; BioCryst: Other: Clinical Trial Committees; Janssen: Consultancy; Kura: Consultancy, Other: Clinical Trial Committees; Geron: Other: Clinical Trial Committees; Astellas: Consultancy; ADC Therapeutics: Research Funding; Agios: Consultancy; Jazz: Consultancy; Pfizer: Other: Travel support, Research Funding; AbbVie: Consultancy, Other: Clinical Trial Committees, Research Funding. Radich: Amgen: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Bhatt: National Marrow Donor Program: Research Funding; Tolero Pharmaceuticals, Inc: Research Funding; Pfizer: Research Funding; Incyte: Consultancy, Research Funding; Jazz: Research Funding; Abbvie: Consultancy, Research Funding; Partnership for health analytic research, LLC: Consultancy; Servier Pharmaceuticals LLC: Consultancy; Rigel: Consultancy; Abbvie: Consultancy, Research Funding; Genentech: Consultancy. Luger: Syros: Honoraria; Agios: Honoraria; Daiichi Sankyo: Honoraria; Jazz Pharmaceuticals: Honoraria; Brystol Myers Squibb: Honoraria; Acceleron: Honoraria; Astellas: Honoraria; Pfizer: Honoraria; Onconova: Research Funding; Celgene: Research Funding; Biosight: Research Funding; Hoffman LaRoche: Research Funding; Kura: Research Funding. Litzow: Omeros: Other: Advisory Board; Astellas: Research Funding; Jazz: Other: Advisory Board; Amgen: Research Funding; Pluristem: Research Funding; Biosight: Other: Data monitoring committee; Actinium: Research Funding; AbbVie: Research Funding. OffLabel Disclosure: Pembrolizumab has not been approved for the treatment of CML

Abstract Background Inhibition of PD-L1 with atezolizumab combined with chemotherapy has shown acceptable safety and improved survival in patients with metastatic PD-L1 positive triple negative breast cancer (TNBC). Patients with TNBC who do not achieve a pathological complete response (pCR) to neoadjuvant chemotherapy have a high risk of disease recurrence and death. This randomized, open-label, phase 2 trial evaluates neoadjuvant carboplatin and paclitaxel with or without atezolizumab in patients with previously untreated clinical stages II and III TNBC. Methods Women aged ≥18 years with clinical stage T2-T4c, any N, M0 primary tumor by AJCC 7th edition staging TNBC; ECOG PS 0-2; and no prior systemic therapy for the indexed breast cancer were eligible. Patients were randomized in a 1:2 ratio to carboplatin AUC5 q 3 weeks x 4 + paclitaxel 80 mg/m2 q week x 12 (Arm A), or carboplatin AUC5 q 3 weeks x 4 + paclitaxel 80 mg/m2 q week x 12 + atezolizumab 1200 mg q3 weeks x 4 (Arm B). Surgery was 3-6 weeks following neoadjuvant chemotherapy. Adjuvant dose-dense doxorubicin and cyclophosphamide was administered q2 weeks with growth factor support to all patients as per routine care. pCR and tumor infiltrating lymphocyte (TIL) percentages are the co-primary endpoints. pCR-evaluable population includes all eligible women who have been randomized and received at least one dose of combination therapy, while the TIL-evaluable population includes all eligible women who have evaluable TIL percentage after one cycle of therapy. A sample size of 67 (22 in Arm A, and 45 in Arm B) provided 80% power at 1-sided alpha = 0.10 to detect a minimum of 15% difference in TIL and 29% improvement (40% vs. 69%) in pCR, respectively. Herein, we report pCR results in the per protocol modified intent-to-treat population (mITT), which includes all eligible patients who were randomized and received at least one dose of combination therapy. Results Sixty-seven patients were randomized between 8/2017 and 9/2019. Six patients randomized to Arm A withdrew consent; 2 of these received protocol therapy but are excluded from the mITT analyses as they are not evaluable because definitive pathology reports are not available. Median follow up is 6 months (range 0.3 - 12.6 months). Median age is 52 years (range 25 - 78). Forty-three (64.2%) were Caucasian and thirteen (19.4%) were African American. Twenty-five (37.3%) were pre-menopausal. 67.2% and 32.8% had stages II and III disease respectively. Nine (13.4%) had a germline mutation in either BRCA1 or BRCA2. In the mITT population, 3 of 16 patients achieved pCR in Arm A - 18.8% (95% CI 4.0%- 45.6%), versus 25 of 45 patients in Arm B - 55.6% (95% CI 40.0%-70.4%); p value 0.018. pCR in those with BRCA mutations was 50% and 80% in Arm A and Arm B, respectively. Treatment delays were observed in 9 patients (40.9%) in Arm A, and 20 (44.4%) in Arm B; dose reductions occurred in 4 patients (18.1%) in Arm A, and in 6 (13.3%) in Arm B. There were 4 SAEs in Arm A and 10 in Arm B. One patient in Arm B had grade 3 adrenal insufficiency. One patient in Arm B died from recurrent disease during the follow-up period. Conclusions: The addition of atezolizumab to neoadjuvant carboplatin and paclitaxel resulted in an increased pCR rate in patients with clinical stages II and III TNBC. However, the pCR in the control Arm A was lower than expected, possibly due to the absence of neoadjuvant anthracyclines. The high pCR rate observed in the experimental arm of this study is similar to that observed in other neoadjuvant trials utilizing anthracyclines, taxanes, and carboplatin in TNBC. Clinical trial information: NCT02883062. Citation Format: Foluso O Ademuyiwa, Feng Gao, Ina Chen, Donald W Northfelt, Robert Wesolowski, Mili Arora, Adam Brufsky, Claire Dees, Cesar A Santa-Maria, Roisin M Connolly, Jeremy Force, Alvaro Moreno-Aspitia, Sarah Larson, Elad Sharon, William Gillanders. Nci 10013 - A randomized phase 2 study of neoadjuvant carboplatin and paclitaxel, with or without atezolizumab in triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD14-09.