To perform a retrospective analysis to assess the utility of pretreatment serum prostatic acid phosphatase (PAP) as a predictor of cause-specific survival (CSS) in patients with higher risk prostate cancer treated with palladium-103 (¹⁰³Pd) brachytherapy and supplemental external beam radiotherapy (EBRT).

From 1992 to 1996, 193 patients with clinically localized prostate adenocarcinoma, a pretreatment PAP level, and Gleason score 7 or more, and/or a prostate-specific antigen (PSA) level of 10 ng/mL or more were treated with ¹⁰³Pd brachytherapy and supplemental EBRT. The patients underwent EBRT of 41.4 Gy to a limited pelvic field and ¹⁰³Pd brachytherapy with a prescribed minimum ¹⁰³Pd dose of 80 Gy. Multivariate analysis was performed to analyze the predictive value of PAP, PSA, and Gleason score on CSS.

The 10-year CSS rate for patients with a PAP level of less than 1.5, 1.5 to 2.4, and 2.5 U/L or more was 93%, 87%, and 75%, respectively (P = 0.013). The 10-year CSS rate for patients with a PSA level of less than 10, 10 to 20, and greater than 20 ng/mL was 92%, 76%, and 83%, respectively (P = 0.393). The 10-year CSS rate for patients with a Gleason score of 6, 7, 8, and 9 was 90%, 89%, 70%, and 68%, respectively (P = 0.002). On Cox multivariate regression analysis, PAP (hazard ratio 1.31, P <0.0001) and Gleason score (hazard ratio 2.37, P = 0.0007) were associated with CSS. PSA was not predictive of CSS (P = 0.393).

The results of this study demonstrated that PAP is a stronger predictor of CSS than PSA or Gleason score in men with higher risk prostate cancer treated with ¹⁰³Pd brachytherapy and EBRT. Given the findings of this analysis, the use of PAP should be reconsidered in these patients.