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.