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

PURPOSE We recently identified a progression-fi ee survival advantage for c linically localized high-risk prostate cancer patients receiving whole-pelv ic irradiation. We now seek to identify a subgroup most likely to benefit f rom whole-pelvic irradiation. METHODS Between October 1987 and December 1995, 506 clinically localized pr ostate 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-specif ic antigen (PSA) failure was defined as (1) a PSA value greater than or equ al to 1 ng/mT, or (2) a PSA value that rose 2 0.5 ng/mL in less than or equ al to I year posttreatment on two consecutive measurements, with the first rise defined as the dme of failure. The calculated risk of lymph node posit ivity (%rLN+) was defined as (2)/(3)(initial PSA) + 10(Gleason score - 6), with intermediate risk defined as 15% I %rLN+ < 35% and highest risk. defin ed as %rLN+ greater than or equal to 35%. Univariate and multivariate analy ses ses were performed. RESULTS Intermediate-risk patients receiving whole-pelvic irradiation had s ignificantly improved freedom from PSA failure compared with those receivin g prostatic irradiation only (median progression-free survival 39.5 months vs 22.5 months; P < 0.0001); highest-risk patients did not (median progress ion-free survival 27.2 months vs 20.8 months, P = NS). Multivariate analysi s revealed type of radiation treatment to be the most significant independe nt predictor of outcome (P < 0.0001), DISCUSSIONS Whole-pelvic radiotherapy most significantly improves the PSA f ailure-free survival in patients with an intermediate calculated risk of ly mph node positivity, suggesting that highest-risk patients may present with distant mt crometastases.