PD-L1 Expression Reveals Significant Association With Squamous Differentiation in Upper Tract Urothelial Carcinoma.

<bold>Objectives: </bold>Limited literature is available on the tumor microenvironment (TM) of upper tract urothelial carcinoma (UTUC). This study comprehensively reviews programmed death 1 receptor (PD-1)-positive and CD8+ tumor-infiltrating lymphocytes (TILs) and programmed death ligand 1 (PD-L1) expression on tumor epithelium (TE).<bold>Methods: </bold>Seventy-two nephroureterectomy specimens were analyzed for PD-L1, PD-1, and CD8. One percent or more tumor and lymphohistiocyte PD-L1 expression was considered positive. TIL density by H&E was scored semiquantitatively from 0 to 3, and CD8+ and PD-1+ TILs were quantified in hotspots.<bold>Results: </bold>Of the cases, 37.5% demonstrated PD-L1+ on TE. PD-L1+ TE showed an association with pathologic stage (P = .01), squamous differentiation (SqD) (P < .001), TILs by H&E (P = .02), PD-1+ peritumoral TILs (P = .01), and PD-L1+ peritumoral lymphohistiocytes (P = .002). Finally, there was a significant difference in PD-1+ peritumoral TILs in cases with SqD vs no SqD (P = .03).<bold>Conclusions: </bold>Aggressive UTUC is associated with a distinct TM. Furthermore, TM of UTUC-SqD was distinctly different from those with no SqD, warranting study in a larger cohort. [ABSTRACT FROM AUTHOR]