The prognostic significance of a single serum prostate-specific antigen value beyond six months after radiation therapy for adenocarcinoma of the prostate

Purpose: The aim of this study was to define criteria for interpreting a single serum prostate-specific antigen (PSA) level measured at 6 months to 5 years after definitive radiotherapy for prostate cancer. Methods and Materials: Two hundred and ninety-two patients with Stages A2 to C prostate cancer treated with radiotherapy only and followed up with multiple PSA determinations were studied. The patients were stratified into PSA strata based on the highest PSA level recroved for each patient at 6 to 60 months after treatment. The PSA strata and the number of patients in each were: (a) PSA ≤ 1 ng/ml, 114 patients; (b) PSA > 1, but ≤ 2 ng/ml, 60 patients; (c) PSA > 2, but ≤ 4 ng/ml, 48 patients; (d) PSA > 4, but ≤ 10 ng/ml, 47 patients; (e) PSA > 10 ng/ml, 23 patients. Desease outcome specified as relapse, rising PSA profile or both was evaluated in each PSA stratum. Results: The actuarial 3-year incidence of relapse in each PSA stratum was: (a) 5%; (b) 0%; (c) 12%; (d) 31%; and, (e) 84%. If the occurrence of a rising PSA profile was included as an endpoint then the incidence of relapse or rising PSA at 3 years in each PSA stratum was: (a) 5%; (b) 14%; (c) 45%; (d) 84%; and, (e) 100%. Patients with the a highest late PSA value ≤ 4 ng/ml had a 20% incidence of relapse or rising PSA at 4 years; patients with a highest late PSA value > 4 ng/ml had a 90% incidence of relapse or rising PSA at 3 years. Conclusion: A PSA level of 4 ng/ml is a good criterion for prognostication of a single PSA level obtained at 6 months to 5 years after radiotherapy. Patients whose PSA level in that time interval exceeds 4 ng/ml have a poor outcome.