Infrequent involvement of the anterior base in low-risk patients with clinically localized prostate cancer and its possible significance in definitive radiation therapy.

Background: The zonal distribution and location of tumors in different subgroups of Japanese patients with clinically localized prostate cancer have not been fully described. The appropriate radiation treatment volume thus remains unclear. Methods: Radical prostatectomy specimens of 141 consecutive patients with clinically localized prostate cancer were examined by the whole organ step-section technique. The zonal distribution and location of tumors at different levels of the gland were investigated after stratification into patient subgroups based on preoperative clinicopathological findings and risk group assessment. Results: The median tumor volume was 2.8 cm(3); 72 patients (51.1%) had pathologically organ-confined disease (pT2). Higher risk groups showed a statistically significant increase in tumor volume and a decrease in the rate of pathologically confirmed organ confinement. Involvement of the anterior base was found infrequently in certain patient subgroups: in only one of 20 patients (5%) with preoperative PSA <4.0 ng/ml, in three of 19 patients (15.8%) with specimen Gleason scores of 2-4 and in two of 32 patients (6.3%) identified as low-risk. Conclusions: Infrequent involvement of the anterior base in low-risk patients may be an intrinsic feature of clinically localized prostate cancer. Treatment volume modifications in these patients that reduce the radiation dose to the anterior base may be justified to avoid acute and late genitourinary toxicities.