Impact of Histological Variants on Clinical Responses to Pembrolizumab in Patients With Metastatic Urothelial Cancer.

BACKGROUND: The efficacy of anti-programmed celldeath protein 1 treatment in patients with urothelial carcinoma (UC) with molecular subtypes of histological variants has not been investigated. This study aimed to examine the impact of histological variants classified according to molecular subtypes on clinical outcomes in patients with platinum-resistant metastatic UC treated with pembrolizumab. PATIENTS AND METHODS: Data of 168 patients with metastatic UC who received intravenous pembrolizumab after platinum-based chemotherapy between December 2017 and November 2020 were retrospectively reviewed. Relationships between histological variant type (basal or luminal molecular subtypes) and survival outcome and response to immunotherapy were examined. Clinicopathological factors were analyzed using the Cox proportional hazards model. RESULTS: UC with histological variants was identified in 19 (11.3%) cases (basal subtype in 12; luminal subtype in 7). The median age of the patients was 72.5 years (range=40-89 years). The performance status was 0-1 in 151 (89.9%) patients. Liver metastasis was detected in 44 (26.2%) patients. The median progression-free survival was 3.5 months (range=0.5-34.3 months). Treatment with immune checkpoint inhibitors resulted in an overall mean survival (from the start of treatment) of 8.1 months (range=1.2-34.3 months). Patients with basal-type UC had significantly shorter progression-free survival and cancer-specific survival than those with pure UC (p=0.010 and p=0.035, respectively). A complete response was observed in eight patients (seven with pure UC, one with basal type). CONCLUSION: The basal histological variant might be a potential prognostic indicator in patients with platinum-resistant metastatic UC treated with pembrolizumab.