Predictors of response to immune checkpoint inhibition in a real world gynecologic cancer population

•Previously treated gynecologic clear cell tumors had a CPI response rate of 57% despite MSI stable status.•Immune related adverse events occurred in 40.3% of patients.•Patients who developed immune toxicity had higher ORR, PFS and OS.•In chemo-naïve MSI-H recurrent endometrial carcinoma ORR to CPI was 83%. Prognostic factors for immune checkpoint inhibitor (CPI) response in gynecologic cancer are limited. This retrospective study aimed to identify prognostic factors associated with improved overall response rate (ORR) and progression free survival (PFS) in gynecologic cancer patients receiving at least two cycles of CPI. PFS was compared by univariate cox regressions. Univariate and multivariable analyses were used for prognostic factors of PFS and ORR. 72 patients were identified (20 ovarian, 36 endometrial, 13 cervix, 1 vaginal, 2 others). Immune related adverse events (IRAE) occurred in 40.3% of patients (29/72). IRAE was associated with higher ORR (44.8% IRAE vs 20.9% no IRAE, OR 3.1, p = 0.024), improved PFS (12.9 m IRAE vs 4.7 m no IRAE, HR 0.43, p = 0.004) and improved OS (22.9 m IRAE vs 12.2 m no IRAE, HR 0.47, p = 0.021). Additionally, Clear cell histology had superior ORR compared to MSI stable endometrial and ovarian cancers (ORR 57.1% vs 11.8%, OR 10.0, p = 0.032). Responders more often had ARIDIA mutation, PI3K/PTEN alteration and less often had a P53 mutation. In a subset of six MSI-H, recurrent, chemo-naive endometrial cancer ORR was 83.3%. Overall, we found favorable outcomes after CPI for clear cell tumors and patients who developed IRAE. Additionally, first-line systemic therapy with CPI in recurrent MSI-H endometrial cancer had encouraging ORR with durable responses.