Objectives. To evaluate the relationship between the postprostatectomy prostate-specific antigen (PSA) nadir and the outcome of patients with salvage radiotherapy. Methods. Seventy-eight patients received definitive external beam radiation for recurrence following radical prostatectomy (RP). The PSA nadir was undetectable in 41 patients (less than 0.05 ng/ml). All patients received salvage radiotherapy (median dose 66 Gy) for a median of 19 months (range 2 to 149) following prostatectomy. The median follow-up time was 25 months (range 1 to 59) from the date of completion of radiation. Results. Among patients having an undetectable or detectable postoperative PSA, 78% and 68% were free of disease, respectively, at the last follow-up. At 3 years, the disease-free survival rate were 65% and 60%, respectively (P = 0.6). Overall, the disease-free survival rate at 3 years was 78% in patients with a PSA level 2 ng/ml or less at the time of radiotherapy compared to 31% with a PSA greater than 2 ng/ml (P <0.0001). Conclusions. Many patients who never achieve an undetectable postprostatectomy PSA level may still be salvaged with therapeutic radiotherapy. The best predictor of a favorable outcome is a low (2 ng/ml or less) PSA level at the time of radiation.
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