Expression of p21 cell cycle protein is an independent predictor of response to salvage radiotherapy after radical prostatectomy.

Background: To assess whether the expression of p21, p27, and p53 could predict biochemical failure in prostate cancer patients treated with neoadjuvant androgen deprivation prior to salvage radiotherapy for a rising post-radical prostatectomy (RP) prostate-specific antigen (PSA).

Methods: The expression of p21, p27, and p53 was determined by immunohistochemistry in a cohort of 74 formalin-fixed paraffin-embedded prostate cancer samples obtained from RP. Expression of these markers was then correlated with clinicopathological parameters and biochemical failure-free survival after salvage radiotherapy.

Results: Expression of p21, p27, and p53 was observed in 20%, 69%, and 74% of prostate cancer specimens, respectively. Overexpression of p21 correlated with a higher Gleason score (>7) (P = 0.024). Of the three markers, only p21 expression was correlated with PSA failure after radiotherapy (P = 0.034). In multivariate analysis, both positive p21 (P = 0.004) and pre-radiation serum PSA > 1 ng/ml (P < 0.0001) were independent predictors of biochemical failure after salvage radiotherapy. Patients with p21- tumors and a serum PSA level < or = 1 ng/ml before salvage radiotherapy had a biochemical failure-free survival at 5 years of 83%, compared to 16% at 5 years for those patients with either p21+ tumor or a PSA > 1 ng/ml. Patients with both p21+ and a PSA level > 1 ng/ml had a much lower biochemical failure-free survival rate of 25% at only 18 months (P < 0.0001).

Conclusions: The expression of p21 in prostatectomy specimens could help predict the likelihood of response to salvage radiotherapy, particularly in patients treated before PSA reaches 1 ng/ml.