Patterns of Local Failure following Radiation Therapy for Prostate Cancer

Purpose: Little is known about patterns of local failure following radiation therapy for prostate cancer. We aimed to characterize post-radiation biopsy findings, including the treatment effect and the zonal distribution of recurrent disease after radiation therapy, in men experiencing biochemical recurrence. Materials and Methods: We identified patients who received post-radiation biopsy in the setting of biochemical recurrence following primary radiation for localized disease. Histological post-radiation biopsy results were categorized by the absence of tumor, demonstration of radiation treatment effect, failure (recurrent cancer) or a combination of treatment effect and failure. We described patterns of histological failure and compared them to the diagnostic biopsy findings. Results: A total of 284 men underwent mapped post-radiation biopsy for biochemical recurrence. Mean age at initial diagnosis was 63 years and median prostate specific antigen was 8.2 ng/ml. Of the men 33%, 32% and 35% were classified at low, intermediate and high risk based on clinical CAPRA (Cancer of the Prostate Risk Assessment) categories. Median time to post-radiation biopsy was 61 months after treatment. Findings were negative in 4% of cases while we noted a treatment effect in 31%, failure in 45% and a combination in 20%. Failure rates were similar across sextants. Of 140 patients with mapped pretreatment and posttreatment biopsies 4% demonstrated cancer in a new location previously identified as negative. Gleason upgrading occurred in 43% of cases with 85% upgraded to 4 + 3 or higher. Conclusions: Men with rising prostate specific antigen after radiotherapy for prostate cancer most often experience recurrence in dominant tumor sites. Whether failure is due to inadequate targeting, dosing or intrinsic radiation resistance remains unknown to our knowledge. Further study is warranted.