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BACKGROUND We evaluated the combination of retifanlimab, INCAGN01876, and FSRT in patients with recurrent GBM. METHODS Phase II, single-center, 2 cohort study (A: single-arm non-surgical cohort; B, two-arm neoadjuvant/surgical cohort). Cohort A patients received pre-FSRT one-time doses of retifanlimab (500mg) and INCAGN01876 (300mg), FSRT (8 Gy x 3 fractions), and post-FSRT 28-day treatment cycles (retifanlimab, day 1; INCAGN01876, days 1, 15). Cohort B patients received pre-surgery doses of retifanlimab + INCAGN01876; subsequently, patients either went directly to resection (Sub-Arm 1) or to FSRT followed by resection (Sub-Arm 2). All patients resumed immunotherapy post-operatively. Primary endpoint: ORR in Cohort A. Data cut-off for this analysis was June 30, 2022. RESULTS Thirty-two evaluable patients: Cohort A, n=16; Cohort B, n=16 (Sub-Arm 1, n=8, Sub-Arm 2, n=8). Median follow-up time: Cohort A, 13.6 months; Cohort B, 8.8 months. Forty-four percent women, median age 64 (IQR, 55–65), 56% MGMT unmethylated. Most common grade 3/4 treatment-related AEs included cerebral edema (25%), lymphopenia (16%), and cognitive disturbance (13%). Efficacy in Cohort A: no objective responses observed, best response of stable disease achieved in 9/16 patients (56%), median PFS 3.9 months (95% CI 2.1 – 6.2 months), median OS 9.8 months (95% CI 8.3 months – not reached [NR]). Efficacy in Cohort B: median PFS NR, median OS 15.1 months (95% CI 8.5 months – NR). Median PFS and OS are longer in Cohort B Sub-Arm 2 compared to Cohort B Sub-Arm 1 (PFS, NR vs. 2.2 months, p = 0.009; OS, NR vs. 8.5 months, p=0.026). Results of tissue and blood-based immune correlative analyses will be presented. CONCLUSIONS The combination of retifanlimab, INCAGN01876, and FSRT is generally well-tolerated in patients with recurrent GBM when administered with or without surgical resection. Survival outcomes in the neoadjuvant cohort are encouraging, largely driven by patients that received neoadjuvant FSRT.

e20019 Background: The anti-CTLA4 antibody, ipi, improves survival in metastatic melanoma. Combined radiotherapy (RT) and ipi may increase immune response to improve outcomes but also increase toxi...

BACKGROUND: Ipilumumab (Ipi), an antibody that enhances T-cell activation, has been shown to improve survival in patients with metastatic melanoma. Ipilumumab may have synergistic effects with radiotherapy but this may result in increased toxicity. This study investigated the incidence of acute radiation effect (ARE) in patients with melanoma brain metastases treated with Ipi and radiosurgery (SRS) or whole brain radiotherapy (WBRT). METHODOLOGY: This retrospective study included metastatic melanoma patients treated at our institution from 2008-2013 who received SRS or WBRT for brain metastases within 4 months of Ipi treatment. We evaluated the incidence, timing and factors associated with acute radiation effect (ARE). RESULTS: From 159 patients treated with Ipi, 22 patients also received brain RT within 4 months of treatment. Three patients were excluded for lack of follow-up brain imaging, thus 19 were analysed: 14 males and 5 females, with median age 58 years (range 24-82). Ten were treated with SRS, 7 with WBRT, and 2 with SRS plus WBRT. Median dose for SRS was 21 Gy (range: 15-24 Gy). Five of 13 patients treated with SRS (38%) experienced symptomatic edema requiring steroids within 1 month of starting Ipi, and within 4 months of RT. One patient had a haemorrhage and 1 required surgical resection, which demonstrated viable disease. Therefore 3 patients (23%) treated with SRS developed isolated ARE. These metastases had volumes less than 4.2 cm3 and were treated within 4 months of Ipi to a median dose of 19.5 Gy (range 15-21 Gy). No patients with WBRT alone developed ARE. CONCLUSIONS: Following SRS for brain mets and Ipi, ARE was seen in 23% of patients within 4 months of starting Ipi treatment. This is greater than the commonly reported 10% risk of ARE after SRS alone for brain metastasis. No increased toxicity was seen with WBRT and Ipi.