Prostate cancer in a large prostate is associated with a decreased prostate specific antigen failure rate after brachytherapy

Purpose: A large prostate has been found to correlate with improved prostate cancer survival in men undergoing radical prostatectomy. In the current study we analyzed the relationship of prostate size and prostate specific antigen (PSA) failure in men undergoing brachytherapy for localized prostate cancer. Materials and Methods: We studied data on 613 men who had undergone I-125 radioactive seed implantation. Average patient age +/- SD was 65 +/- 7.2 years. Average prostate volume ultrasonically measured at seed insertion was 40 +/- 15 ml. All patients had a minimum of 2 years of followup. Results: Men with a large prostate had increased freedom from failure compared to men with a small prostate. Failure time in men with an intermediate size prostate was between that for large and small prostates. This difference in failure rates was significant (log rank test p = 0.0002). We further analyzed our data with Cox regression. Large prostate size significantly correlated with increased time to PSA failure (p = 0.013) and it was independent of the significant effects of Gleason score, PSA, disease stage (p <0.001), minimal radiation dose covering 90% of prostate volume (p = 0.008) and hormone treatment, including androgen ablation (p = 0.001). Conclusions: Some investigators have postulated that paracrine signals acting to regulate epithelial proliferation in benign prostatic hypertrophy have beneficial influences on coexistent prostate cancer. Our finding that the effect of prostate size is independent of Gleason score, PSA and disease stage supports the paracrine signal mechanism. If a circulating substance, such as a cytokine, might be responsible for improved survival, this substance might be useful for treating prostate cancer. Moreover, since we found that prostate size is independent of PSA, Gleason score and tumor stage for predicting outcome, we hypothesize that patients with a small prostate treated with brachytherapy might benefit from hormone treatment and larger radiation doses. These measures are now generally reserved for men with more advanced tumors, higher PSA and increased Gleason scores.