Prognostic Implications of Aberrations in p16/pRb Pathway in Urothelial Bladder Carcinomas: A Multivariate Analysis Including p53 Expression and Proliferation Markers

Objective: To assess the prognostic value of the expression of two negative regulators of the cell cycle, namely CDKN2/INK4a gene product (p16) and retinoblastoma gene product (pRb), in urinary bladder cancer in relation to clinicopathological parameters, proliferative fraction and p53 protein accumulation. Methods: Paraffin sections from 139 patients with urothelial carcinomas were stained immunohistochemically with antibodies to p16 (F12), pRb (PMG3–245), p53 (DO1), PCNA (PC10) and Ki–67 (MIB–1). Results: Diminished p16 and pRb expression occurred in 29 and 74% of cases, respectively, being associated with advanced stage but not with histological grade, papillary status or proliferation rate. In most cases (53%) with some fault in the p16/pRb pathway, only one gene was affected. A double–negative p16/pRb phenotype was comparatively uncommon (25%) and was usually seen in T3–T4 tumours. In survival analysis (either univariate or multivariate) aberrant p16 expression was an adverse prognostic parameter only in T3–T4 tumours. In contrast, the abnormal p16/pRb and p53/p16 phenotypes were linked to a diminished overall and disease–free survival (univariate analysis); p53/p16 abnormal expression was also found to be an independent predictor of reduced survival in muscle–invasive tumours, while proliferation markers were the only parameters with independent significance in superficial (Ta–T1) tumours. Conclusion: Our results suggest that lack of p16 immunoexpression, when combined with p53 accumulation, plays an important role in determining the clinical outcome in muscle–invasive urothelial carcinomas.