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Prostate-specific antigen and radiation therapy for clinically localized prostate cancer
G K Zagars1, A Pollack, V S Kavadi
1Department of Clinical Radiotherapy, University of Texas, M. D. Anderson Cancer Center, Houston 77030, USA.
Purpose:
This study was undertaken to: (a) define the prognostic significance of pretreatment serum prostate-specific antigen (PSA) levels in localized prostate cancer treated with radiation; (b) define the prognostic usefulness of postradiation PSA levels; (c) evaluate the outcome of radiation using PSA as an endpoint.
Methods And Materials:
Disease outcome in 707 patients with Stages T1 (205 men), T2 (256 men), T3 (239 men), and T4 (7 men), receiving definitive external radiation as sole therapy, was evaluated using univariate and multivariate techniques.
Results:
At a mean follow-up of 31 months, 157 patients (22%) developed relapse or a rising PSA. Multivariate analysis revealed pretreatment PSA level to be the most significant prognostic factor, with lesser though significant contributions due to Gleason grade (2-6 vs. 7-10) and transurethral resection in T3/T4 disease. The following four prognostic groupings were defined: group I, PSA < or = 4 ng/ml, any grade; group II, 4 < PSA < or = 20, grades 2-6; group III, 4 < PSA < or = 20, grades 7-10; group IV, PSA > 20, any grade. Five-year actuarial relapse rates in these groups were: I, 12%; II, 34%; III, 40%; and IV, 81%. Posttreatment nadir PSA was an independent determinant of outcome and only patients with nadir values < 1 ng/ml fared well (5-year relapse rate 20%). Using rising PSA as an endpoint the 461 patients with T1/T2 disease had an actuarial freedom from disease rate of 70% at 5 years, which appeared to plateau, suggesting that many were cured. No plateau was evident for T3/T4 disease.
Conclusion:
Pretreatment serum PSA is the single most important predictor of disease outcome after radiation for local prostate cancer. Tumor grade has a lesser though significant prognostic role. Postirradiation nadir PSA value during the first year is a sensitive indicator of response to treatment. Only nadir values < 1 ng/ml are associated with a favorable outlook. A significant fraction of men with T1/T2 disease may be cured with radiation. There was no evidence for a cured fraction among patients with T3/T4 disease.