Biopsy after external beam radiation therapy for adenocarcinoma of the prostate: correlation with original histological grade and current prostate specific antigen levels

We obtained post-irradiation biopsies in 37 men with initially stage T3 prostatic adenocarcinoma treated by external beam radiotherapy. Eligibility for post-irradiation biopsy included no clinical local failure, interval since treatment of 24 months or more and no endocrine therapy. Of the 37 patients 23 (62%) had negative biopsies while 14 (38%) had positive biopsies. Of 23 patients whose original cancer was well or moderately differentiated 18 (78%) had negative biopsies, compared to only 5 of 14 (36%) of those with poorly differentiated cancer (p less than 0.03). Among 19 patients whose current serum prostate specific antigen (PSA) value is less than 2.5 ng./ml. 15 (79%) had negative biopsies, compared to only 4 of 14 (29%) with a PSA level of greater than 2.5 ng./ml. (p less than 0.02). These results strongly suggest that there is a low probability of positive post-irradiation biopsy regardless of its significance in men with a normal prostate by palpation and a normal serum PSA value. However, short followup since biopsy precludes analysis of the predictive value of post-irradiation biopsy on long-term local and distant disease status.