Immunohistochemical classification using urothelial differentiation markers can stratify prognosis in patients with muscle invasive bladder cancer
Recent genomic studies have revealed that muscle invasive bladder cancer (MIBC) can be classified into intrinsic molecular subtypes. In breast cancer, immunohistochemical (IHC) determination of subtypes is used to guide clinical decision making. Here, we studied IHC classification of MIBC using urothelial differentiation markers.
The study population consisted of 115 patients with MIBC treated with radical cystectomy without neoadjuvant chemotherapy and 10 samples of normal urothelium. The whole sections of MIBC were stained for Uroplakin3 (UPK3), GATA3 and cytokeratin5/6 (CK5/6) by IHC, which were representative molecular markers for the intrinsic subtypes. The definitions of positivity were any cancer cell staining for UPK3, over 20% of cancer cell staining for GATA3, all layers staining for CK5/6.
In normal urothelium, UPK3 expression was observed only in umbrella cells, while CK5/6 expression was detected only in the basal layer. GATA3 expression was detected in almost all layers but its expression was higher in intermediate cells. Positive staining for UPK3, GATA3, CK5/6 was detected in 30 (26%), 92 (80%) and 37 (32%) of all MIBC cases, respectively. The positive rate for UPK3/GATA3/CK5/6 was 53/100/9% in papillary morphology (n=34), 11/67/46% in nodular morphology (n=70), 31/88/23% in pure urothelial carcinoma (UC; n=93), and 6/39/83% in UC with squamous differentiation (n=18), respectively. Patients with UPK3- (P=0.0024), GATA3- (P<0.0001) and CK5/6+ (P=0.0008) and had significantly worse prognosis than those with UPK3+, GATA3+, CK5/6-, respectively. 29/30 (97%) cases of UPK3+ were GATA3+, and UPK3+ and GATA3+ were correlated with CK5/6- (P=0.0027, P<0.0001), suggesting that GATA3+ had overlap with UPK3+ and was nearly mutually exclusive for CK5/6+. From these results, we classified three groups; differentiated (UPK3+), intermediate (UPK3-/GATA3+) and basal (GATA3-/CK5/6/+). The rate of histological grade 3, stage 3-4 and CSS at 5 years in differentiated, intermediate and basal group were 44/58/79% (P=0.065), 30/46/79% (P=0.0041), 96/65/25% (P<0.0001), respectively. In multivariate analysis, IHC classification, stage and tumor morphology were independent prognostic factors for poor prognosis.</p>
Simple IHC classification using urothelial differentiation markers can improve stratification of prognosis in MIBC, which may be useful in routine clinical practice.