Identification of a high-risk clinically localized prostate cancer subgroup receiving maximum benefit from whole-pelvic irradiation.

PURPOSE: We recently identified a progression-free survival advantage for clinically localized high-risk prostate cancer patients receiving whole-pelvic irradiation. We now seek to identify a subgroup most likely to benefit from whole-pelvic irradiation. METHODS: Between October 1987 and December 1995, 506 clinically localized prostate cancer patients were treated with definitive radiotherapy consisting of whole-pelvic irradiation followed by a prostate-only boost, or prostate-only treatment (median follow-up, 35 months vs 30 months). Prostate-specific antigen (PSA) failure was defined as (1) a PSA value > or = 1 ng/mL or (2) a PSA value that rose > or = 0.5 ng/mL in < or = 1 year posttreatment on two consecutive measurements, with the first rise defined as the time of failure. The calculated risk of lymph node positivity (%rLN+) was defined as 2/3 (initial PSA) + 10(Gleason score - 6), with intermediate risk defined as 15% < or = %rLN+ < 35% and highest risk defined as %rLN+ > or = 35%. Univariate and multivariate analyses were performed. RESULTS: Intermediate-risk patients receiving whole-pelvic irradiation had significantly improved freedom from PSA failure compared with those receiving prostatic irradiation only (median progression-free survival 39.5 months vs 22.5 months; P < 0.0001); highest-risk patients did not (median progression-free survival 27.2 months vs 20.8 months, P = NS). Multivariate analysis revealed type of radiation treatment to be the most significant independent predictor of outcome (P < 0.0001). DISCUSSIONS: Whole-pelvic radiotherapy most significantly improves the PSA failure-free survival in patients with an intermediate calculated risk of lymph node positivity, suggesting that highest-risk patients may present with distant micrometastases.