Upper tract urothelial carcinomas (UTUCs) are a rare and unique subset of urothelial carcinoma (UC). Patients with UTUC may qualify for treatment with immune checkpoint inhibitors if their tumor cells express programmed death ligand-1 (PD-L1). While several large studies have looked at PD-L1 expression in UC, most have not investigated UTUC as a separate group, and most have not used Food and Drug Administration approved PD-L1 stains and scoring systems. Moreover, comparison between studies of PD-L1 expression is challenging as a wide variety of different PD-L1 antibody clones, testing platforms, and cutoff values have been used in the literature.
This is a retrospective study of 37 cases of resected UTUC. Representative tissue from each case was compiled into tissue microarrays and immunohistochemical stains for PD-L1 (Dako antibody clones 22C3 and 28-8) were performed. PD-L1 staining was evaluated using several established Food and Drug Administration approved scoring systems: tumor proportion score (TPS), combined positive score, and immune cell score. Associations between PD-L1 expression and clinicopathologic features were investigated.
Overall expression of PD-L1 in UTUC was 29.7% when using a TPS cutoff of ≥1%. Total of, 55.6% of cases with higher pathologic stage (pT3 or pT4) were positive for PD-L1, compared with only 5.3% of cases with lower pathologic stage (pTis, pT1, or pT2; P=0.0011). When using a combined positive score cutoff of ≥10, there was no significant association between tumor stage and PD-L1 expression. There was no association between PD-L1 positivity and tumor grade, tumor location, sex, or age. There was 100% concordance between 22C3 and 28-8 in terms of positivity rate.
Our study using approved testing methods shows that PD-L1 expression in UTUC is more often associated with high pathologic stage, which may reflect an immune response evasion mechanism that UC cells acquire later in disease progression. In addition we show that 29.7% of UTUCs are positive for PD-L1 TPS expression, comparable to the 20% to 30% reported in UC literature. Finally, PD-L1 22C3 and 28-8 clones show similar overall patterns of staining in this setting.