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 therapy on the serum level of prostate-specific antigen (PSA), as measured by an ultrasensitive Yang Proscheck assay in patients with detectable serum PSA and a negative metastatic survey after radical prostatectomy for T1 or T2 prostate cancer.

Methods: Seventeen patients had a detectable 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 vesicourethral anastomosis. All patients were treated by external radiotherapy, receiving 65 Gy on the prostate fossa over 5 weeks for an assumed low volume residual disease. Patients were followed up by determination of serum PSA every 3 months, using the Yang ultrasensitive assay for a mean duration of 14.4 months.

Results: In 17.6% of the patients (3 of 17) PSA became undetectable (less than 0.05 ng/mL) after radiotherapy. Radiotherapy had no impact on PSA in 35.3% (6 of 17). PSA decreased after radiation therapy within 6 months in 47.1% (8 of 17) and for up to 12 months in 2 patients, with a nadir of 0.28 ng/mL. All patients in this group experienced a secondary rise in PSA a mean of 10.6 months (range, 6 to 18 months) after radiotherapy.

Conclusions: External radiotherapy has a limited impact on residual disease after radical prostatectomy, as assessed by its impact on PSA.