Clinical and Biological Activity of Chemoimmunotherapy in Advanced Endometrial Adenocarcinoma: A Phase II Trial of the Big Ten Cancer Research Consortium.

Purpose: The objective of this study was to assess the efficacy and safety of pembrolizumab in combination with standard carboplatin/paclitaxel in patients with advanced endometrial cancer (EC). Patients and Methods: This single-arm, open-label, multi-center phase II study enrolled patients with RECIST measurable advanced EC. Patients could have received < 1 prior platinum-based regimen and < one non-platinum chemotherapy. The primary endpoint was objective response rate (ORR). Planned sample size of 46 subjects provided 80% power to detect 15% ORR improvement compared to historical control rate of 50%. Results: 46 patients were enrolled, and 43 were evaluable for ORR. Median age was 66 (range: 43-86). Thirty-four (73.9%) patients had recurrent and 12 (26.1%) primary metastatic EC. Patients received carboplatin AUC 6, paclitaxel 175mg/m2 and pembrolizumab 200mg IV every 3 weeks for up to 6 cycles. ORR was 74.4% (32/43), higher than historic controls (p = 0.001). Median PFS was 10.6 months (95% CI 8.3-13.9 months). The most common grade 1-2 treatment related adverse event (TRAEs) included anemia (56.5%), alopecia (47.8%), fatigue (47.8%) and neuropathy (13%), while the most common grade 3-4 TRAEs were lymphopenia, leukopenia, and anemia (19.6% each). High-dimensional spectral flow cytometry (CyTEK) identified enrichment in peripheral CD8+ and CD4+ T cell populations at baseline in responders. The CD8+ T cell compartment in responders exhibited greater expression levels of PD-1 and PD-L1 and higher abundance of effector memory CD8+ cells compared to non-responders. Conclusions: Addition of pembrolizumab to carboplatin and paclitaxel for advanced EC was tolerated and improved ORR compared to historical outcomes.