Immunohistochemistry for p16, but not Rb or p21, is an independent predictor of prognosis in conservatively treated, clinically localised prostate cancer

Aims: Treatment decisions are difficult in clinically localised prostate cancer and further biomarkers of aggressive behaviour are required. We investigated the hypothesis that the tissue expression of three cell cycle markers, Rb, p21 and p16, would provide helpful prognostic information in a well characterised series of prostate cancers which were clinically localised and treated conservatively. Methods: The immunohistochemical staining expression of these markers was assessed in tissue microarrays and correlated with 10 year prostate cancer survival and overall survival and then compared with pathological data including contemporary Gleason score, age, measures of tumour extent and initial serum prostate specific antigen (PSA) level. Results: Rb overexpression did not show any significant association with Gleason score or prostate cancer survival. p21 protein expression showed a significant association with prostate cancer survival (p = 0.02) and overall survival (p = 0.01) in a univariate model but not in a multivariate model with pathological and serum PSA data. There was a significant association between p16 cytoplasmic expression and prostate cancer survival (HR = 2.52, 95% CI = 1.79-3.55, p < 0.001) and overall survival (HR = 1.54, 95% CI = 1.20-1.98, p = 0.001) in a univariate model. p16 expression remained an independent prognostic factor for prostate cancer survival (HR = 1.50, 95% CI = 1.05-2.14, p = 0.03). Conclusion: We conclude that p16 cytoplasmic expression can be used as a predictor of outcome in conservatively treated prostate cancer. Rb and p21 show no independent association with outcome and therefore further research is not warranted.