Pembrolizumab in Patients with Advanced Miscellaneous Rare Cancers: Results from a Phase 2 Basket Trial.

INTRODUCTION

Rare solid tumors account for one-quarter of cancers among adults in the United States, but few resources have been devoted to their treatment. We evaluated the efficacy of pembrolizumab, a programmed cell death-1 inhibitor, in patients with rare solid tumors.

METHODS

We conducted a phase 2 basket trial that included patients with rare, advanced tumors. Patients were enrolled in the study in nine tumor-specific and a 10th cohort of miscellaneous rare histologies. Patients received pembrolizumab 200 mg intravenously every 21 days. The primary endpoint was the non-progression rate at 27 weeks per immune-related Response Evaluation Criteria in Solid Tumors (RECIST). The secondary endpoints were confirmed objective response (immune-related complete response [irCR] or partial response [irPR]), clinical benefit (irCR, irPR, or immune-related stable disease [irSD] ≥ 4 months), safety, and tolerability. Pretreatment biopsy specimens were examined for programmed cell death ligand-1 combined positive score (CPS) and tumor-infiltrating lymphocyte status. Herein, we report the outcomes in 12 patients with miscellaneous rare histologies who were on the study between October 5, 2016, and August 30, 2019.

RESULTS

Twelve patients with rare cancers were enrolled from October 5, 2016, to August 30, 2019. The patients received a median of four lines of therapy before enrollment. Three patients (25%) remained free of progression at 27 weeks, one patient (8%) had an objective response, and five patients (42%) received clinical benefit. Six patients (50%) experienced at least one adverse event, of whom five (42%) experienced immune-related adverse events. The only grade ≥ 3 adverse event was non-immune-related anemia. Among the seven patients with CPS ≥ 1, one had irPR and two had irSD as the best response. Among the six patients with a CPS of 3, one had irPR and two had irSD as the best response.

CONCLUSIONS

Single-agent pembrolizumab showed modest efficacy and was well tolerated in patients with rare solid tumors (ClinicalTrials.gov Identifier: NCT02721732).