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.