Association of current molecular subtypes in urothelial carcinoma with patterns of muscularis propria invasion

Urothelial carcinoma is subdivided into luminal (L), basal (B), and p53-wild-type (WT) molecular subtypes, with basal and p53-WT groups showing more aggressive course and poor treatment response, respectively. The literature on molecular subtypes of UC includes a mixture of different stages. We investigated the molecular profile and outcome of pure cohort of muscle invasive bladder carcinoma (MIBC) considering two distinct patterns of muscularis propria (MP) invasion. Forty-three cystectomies harboring stage pT2 were retrospectively identified in 18 years. MP invasion was subclassified into patterns 1 (tumor encasing intact detrusor muscle bundles) and 2 (tumor dissecting/replacing detrusor muscle). Using IHC, B/L phenotypes, p53, and Ki67 were assessed, and survival data was collected. Pattern 1 invasion was noted in 16 (37%) and pattern 2 in 27 (63%), with mean age of pattern 1 being 10 years younger. B/L phenotypes were successfully determined in 83.7%; 48.8% and 34.8% revealed L and B phenotypes, respectively (indeterminate phenotype in 16.4%). Pattern 1 was associated with L phenotype (GATA3 and HER-2 expressions: p = 0.02 & p = 0.04, respectively). Ki67 ≥ 5/10HPF was noted in pattern 2 and B phenotype (p = 0.03). B phenotype showed association with p53-WT (p = 0.007). In median follow-up of 60.7 months, 63.6% of pattern 1 cases were alive without disease compared to 32% of pattern 2 (not significant). A panel of CK20 and GATA3 for luminal and CK5/6 and CK14 for basal subtypes can provide reliable molecular classification in UC. Also, morphology of MIBC can predict the molecular phenotype and the behavior of the UC.