Clinical significance of CD44 variant 9 expression as a prognostic indicator in bladder cancer

CD44, a major surface receptor for hyaluronic acid, has multiple isoforms and represents a major cancer stem cell marker for various epithelial tumors. CD44 variant 9 (CD44v9) was correlated with recurrence and metastasis in gastric and colon cancer. We examined its role in invasion and as a biomarker for the basal muscle invasive molecular subtype showing worse prognosis, and for tumor progression in high risk (pT1/high grade) non-muscle invasive bladder cancers (NMIBCs). CD44v9, cytokeratin 5/6 (CK5/6), and cytokeratin 20 (CK20) expression was evaluated by immunohistochemistry in. 98 pathologically confirmed specimens (36 muscle and 62 high-risk non-muscle) and correlated to clinical outcome. In vitro analysis was performed using two human bladder cancer cell lines (HT1376 and 5637). The CD44v9 high-expressing group exhibited significantly lower progression-free and cancer-specific survival rates in both muscle (P=0.0349 and 0.0382, respectively) and non-muscle (P=0.0002 and 0.0079) invasive patients. CD44v9 expression was significantly correlated with CK5/6 (P<0.001), colocalizing at the muscle invasion front but distinctly separated from CK20 in non-muscle invasion. CD44 and CD44v9 siRNA knockdown demonstrated significantly lower Matrigel invasion ability and significantly shorter migration distance (all P<0.01). CD44 and CD44v9 knockdown increased E-cadherin and decreased N-cadherin, snail, and slug epithelial-mesenchymal transition marker protein expression. Thus, higher CD44v9 expression was associated with worse prognosis, likely impacting invasion and migration via the epithelial-mesenchymal transition. Together, these findings suggest that CD44v9 expression might be a useful predictive biomarker in basal-type muscle and high-risk NMIBC.