Efficacy of Pembrolizumab in Patients With Variant Urothelial Carcinoma: A Multicenter Retrospective Study.

INTRODUCTION: Although variant urothelial carcinoma (VUC, defined here as urothelial carcinoma with any histological variant) is a clinically aggressive disease, the efficacy of pembrolizumab against VUC is not well characterized. This study assessed the therapeutic response and survival outcomes in patients with advanced VUC treated with pembrolizumab for unresectable recurrent or metastatic disease. PATIENTS AND METHODS: We retrospectively evaluated 103 patients with advanced bladder and upper urinary tract cancer who received pembrolizumab after failure of platinum-based chemotherapy at 6 institutions between January 2018 and June 2021. Objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) were compared between patients with pure urothelial carcinoma (PUC) and those with VUC. RESULTS: We identified 81 and 22 patients with PUC and VUC, respectively. Squamous differentiation (n = 14) was the most common variant element, followed by glandular differentiation (n = 3) and micropapillary variant (n = 3). Baseline characteristics were comparable between the groups. Patients with VUC showed significantly better ORR (59.1% vs. 29.6%, P = .014) and comparable DCR (68.2% vs. 49.4%, P = .150) compared to those with PUC. There were no significant differences between the PUC and VUC groups with respect to PFS (median 5.0 months vs. 10.4 months, P = .222) or OS (median 13.5 months vs. 23.8 months, P = .497). CONCLUSION: Response of VUC to pembrolizumab was not inferior to that of PUC in patients with advanced-stage bladder and upper urinary tract cancer.