Analysis of pembrolizumab in microsatellite instability high (MSI-H) and deficient mismatch repair (dMMR) non-colorectal patients with metastatic cancer.

Pembrolizumab was approved for the treatment of MSI-H/dMMR solid malignancies in a tumor agnostic approval in 2017. Treatment records for patients harboring MSI-H/dMMR status at our institution treated with pembrolizumab were reviewed for outcomes of duration of treatment, progression free survival, and overall survival. Adverse events and immunotherapy biomarkers of PDL-1 status and tumor mutation burden (TMB) were also assessed. Thirty patients were included: 13 with endometrial cancer, 5 non-colorectal gastrointestinal cancer, 2 ovarian or uterine cancer, 2 breast cancer, and 8 with other malignancies. The median duration of treatment was 11 months (range 0-35). Progression free survival and overall survival were not reached. Five patients (16.7%) experienced immune related adverse events, resulting in discontinuation of pembrolizumab in 3. PDL-1 expression and TMB did not appear to correspond to treatment outcomes. This analysis provides a real-world dataset of MSI-H/dMMR solid tumor patients being treated with pembrolizumab, outcomes of which are consistent with registry trials.