Serum prostate-specific antigen in monitoring the response of carcinoma of the prostate to radiation therapy

In order to assess value of serum prostate-specific antigen (PSA) levels in the monitoring of patients with localized prostatic carcinoma undergoing radical radiation therapy, 146 previously untreated patients were studied. To the prostate 60-70 Gy were administered over 8-9 weeks. Median follow-up was 28 every 3 months during 1st year and every 6 months after. Serum PSA levels were measured prior to radiotherapy. Pre-treatment PSA values exceeded 10 ng/ml in 62%. Initial PSA values were correlated with tumor size and Gleason score. PSA levels decreased 6 months after completion of radiation therapy, compared to initial value in 88.3%. It had fallen to 10 ng/ml or less in 59% with initial abnormal PSA levels. Patients whose initial PSA exceeded 50 ng/ml attained levels of 10 ng/ml or less in only 19%. Only 3/55 with both initial and 6-month PSA values ≤ 10 ng/ml developed metastases. Of 91 patients with initial PSA values over 10 ng/ml 54 had a 6-month PSA level of 10 ng/ml or less, and only 4/54 relapsed. By contrast, 13/37 patients with a 6-month PSA level persistently above 10 ng/ml relapsed. The 3-year relapse-free survival is 85.1% for 6-month PSA level ≤ 10 ng/ml, and 50.2% for patients with persistently elevated PSA values. This difference is highly significant (p<0.0001). The pattern of decline of PSA level was also analyzed: 11/22 patients with initial PSA>10 ng/ml and relative difference between an initial and a 6-month PSA value of less than 50%, developed metastases. By contrast, when relative difference was ≥50%, only 6/69 belonging to this group had local recurrence or developed metastases. The 3-year relapse-free survival rate was significantly superior in latter group (76.9 versus 30.2%, p<0.0001). It is concluded that a PSA value in excess of 10 mg/nl 6 months after radiation therapy or a relative difference between an initial and a 6- month PSA value of less than 50% have a poor prognostic significance and are discriminant criteria to identify a subset of patients with a high risk of relapse who may benefit from early hormonal therapy. (author). 22 refs.; 2 figs.; 4 tabs