Basal-subtype bladder tumours show a 'hot' immunophenotype

Basal and luminal molecular subgroups of muscle-invasive urothelial carcinoma (UC) can be recognised by the use of immunohistochemical markers. Studies have shown that responses to chemotherapy and outcomes differ among these subtypes. High-grade UC of the bladder is an immunogenic neoplasm that induces a substantial intratumoral and peritumoral immune response; the phenotype of infiltrating immune cells may yield prognostic information and predict response to therapy. In this study, we aimed to correlate the immunohistochemical phenotype of high-grade UC with immune microenvironment composition.

Two hundred and thirty-five cases of high-grade UC treated with cystectomy were reviewed. Clinicopathological variables for each case were recorded, and disease-free survival at last follow-up was calculated. Invasive front inflammation and tumour-infiltrating lymphocytes were scored for each case. Two hundred and seven cases were used to construct a triplicate-core tissue microarray (TMA), with sections stained for cytokeratin (CK) 5/6 and GATA3. Of the evaluable cases, 167 were designated as luminal (CK5/6- and GATA3+) and 29 as basal (CK5/6+ and GATA3-). Additional sequential TMA sections were stained for CD3, CD4, CD8, CD20, CD68, CD163, FOXP3, programmed cell death protein 1 (PD-1), and programmed death-ligand 1 (PD-L1) (SP263). Basal-subtype tumours showed a trend towards worse disease-specific survival (P = 0.078). There were statistically significant associations between basal subtype and CD8 expression (P = 0.008), PD-1 expression (P = 0.001), and PD-L1 expression (P = 0.014). Lower CD4/CD8 and increased CD8/FOXP3 ratios (P = 0.047 and P = 0.031, respectively) were also identified in the basal-subtype group.

Basal-subtype high-grade UC has an abundance of CD8+ T cells with increased expression of inhibitory markers, indicative of a 'hot' immunophenotype.