EFFECT OF RADIATION-THERAPY AFTER RADICAL PROSTATECTOMY ON SERUM PROSTATE-SPECIFIC ANTIGEN MEASURED BY AN ULTRASENSITIVE ASSAY

Objectives. To study prospectively the impact of adjuvant radiation th erapy on the serum level of prostate-specific antigen (PSA), as measur ed by an ultrasensitive Yang Proscheck assay in patients with detectab le serum PSA and a negative metastatic survey after radical prostatect omy for T1 or T2 prostate cancer. Methods. Seventeen patients had a de tectable serum PSA (2.40 +/- 2.1 ng/mL; range, 0.5 to 10) by the Yang polyclonal assay 2 to 71 months after radical prostatectomy for P2N0 ( 2 patients) or P3N0 (15 patients) prostate cancer. Metastatic workup ( bone and computed tomography scan) was negative; 9 of 17 patients had a local recurrence documented by a positive biopsy of the vesicourethr al anastomosis. All patients were treated by external radiotherapy, re ceiving 65 Gy on the prostate fossa over 5 weeks for an assumed low vo lume residual disease. Patients were followed up by determination of s erum PSA every 5 months, using the Yang ultrasensitive assay for a mea n duration of 14.4 months. Results. In 17.6% of the patients (5 of 17) PSA became undetectable (less than 0.05 ng/mL) after radiotherapy. Ra diotherapy had no impact on PSA in 35.3% (6 of 17). PSA decreased afte r radiation therapy within 6 months in 47.1% (8 of 17) and for up to 1 2 months in 2 patients, with a nadir of 0.28 ng/mL. All patients in th is group experienced a secondary rise in PSA a mean of 10.6 months (ra nge, 6 to 18 months) after radiotherapy. Conclusions. External radioth erapy has a limited impact on residual disease after radical prostatec tomy, as assessed by its impact on PSA.