The prognostic value of PD‐L1 expression in upper tract urothelial carcinoma varies according to platelet count

Abstract Programmed cell death ligand‐1 (PD‐L1) is a ligand for programmed cell death‐1 (PD‐1) that negatively regulates T‐cell activation and plays a crucial role in suppressing anti‐tumor host immunity. Although PD‐L1 is a promising immunotherapy target in various cancers, including urothelial carcinoma (UC), the prognostic significance of PD‐L1 in UC is unclear. As platelets help protect tumor cells from immune elimination in the circulatory system, we hypothesized that tumor PD‐L1 and circulating platelets might synergistically promote tumor metastasis, and that the prognostic significance of PD‐L1 might vary according to platelet count. We immunohistochemically examined tumor PD‐L1 expression in 271 patients with upper tract UC, which revealed PD‐L1 positivity in 31 of 271 cases (11%). The associations of tumor PD‐L1 expression with outcomes varied among patients with high or low platelet counts (Pinteraction