Greater utility of molecular subtype rather than epithelial‐to‐mesenchymal transition (EMT) markers for prognosis in high‐risk non‐muscle‐invasive (HGT1) bladder cancer

Approximately 75% of bladder cancers are non‐muscle invasive (NMIBC). Of these, up to 53% of cases progress to life‐threatening muscle‐invasive bladder cancer (MIBC). Patients with high‐grade stage T1 (HGT1) NMIBC frequently undergo radical cystectomy (RC), although this represents overtreatment for many. Identification of progressors versus non‐progressors could spare unnecessary treatment. Recent studies have confirmed that urothelial carcinoma is composed of two main molecular subtypes, basal and luminal, with 12% of basal tumours exhibiting epithelial‐to‐mesenchymal transition (EMT). Levels of immune cell infiltration have been shown to be subtype‐specific. Here, we performed immunohistochemistry (IHC) for 11 antibodies relating to molecular subtypes or EMT in 26 cases of HGT1 urothelial carcinoma cases with 6 matched samples subsequently obtained at cystectomy (n = 6; 1 muscle‐invasive, 5 non‐muscle‐invasive; 3 = pTis, 1 = pT1, 1 = pTa) and at recurrence (n = 2, pT2). RNAScope was also conducted in a subset. Expression patterns in HGT1 specimens versus MIBC (pT2+) were examined, and correlated with disease‐specific survival (DSS). Levels of stromal tumour‐infiltrating lymphocytes (sTILs) were assessed manually to determine whether lymphocyte infiltration was associated with DSS and whether differences existed between HGT1 and MIBC. Molecular subtype markers demonstrated increased prognostic potential compared to the EMT markers assessed. Increased expression of the luminal markers FOXA1 and SCUBE2, were found to be significantly associated with better DFS. No EMT markers were significantly associated with DFS. In areas of non‐invasive papillary urothelial carcinoma, but not invasive carcinoma, sTIL levels were found to be significantly associated with DFS. While differences were observed between HGT1 cases that progressed versus those that did not, a larger cohort study is required for validation of these findings. Taken together, an emphasis on molecular subtype markers, rather than EMT markers, may be preferable when studying biomarkers of HGT1 urothelial carcinoma in the future.