Prostate-specific antigen to determine progression-free survival after radiation therapy for localized carcinoma of prostate.

ABSTRACT

Prostate-specific antigen (PSA) levels after radiation therapy will more precisely and objectively identify the presence of persistent prostate carcinoma. We determined the impact of PSA marker levels on progression-free status for 123 patients treated by interstitial implantation (I-125) and 311 patients treated by external beam therapy (XRT) who have been followed for a median of 109 and 51 months, respectively. Actuarial progression-free survival curves were calculated, using standard clinical criteria, and then recalculated, using PSA marker criteria. Sera obtained twelve months or more after the initiation of XRT and twenty-four months or more after the date of I-125 were used for determination of PSA levels. Using normal PSA level (by Hybritech assay < or = 4.0 ng/mL) as the criterion for progression-free status for patients treated by XRT, 35 percent of patients with Stage A2, 20 percent of patients with Stage B1 or B2, and 10 percent of patients with Stage C tumor were progression-free at ten years. The progression-free survival by clinical criteria for Stage A2 and 65 percent, B1 was 40 percent, B2 was 35 percent, and C was 25 percent. Using undetectable PSA level (< or = 0.5 ng/mL) as the criterion, less than 10 percent of patients were progression-free at ten years, regardless of stage, grade; and treatment modality. This information should not be interpreted as indicating that radiation is ineffective therapy for prostate cancer, since clinical control of the disease among men in their eighth decade is a more practical goal than marker control. However, PSA monitoring after radiation therapy and after any local therapy for prostate cancer will provide more precise information on the success of that therapy in ablating disease.