Identification of factors predicting response to adjuvant radiation therapy in patients with positive margins after radical prostatectomy

Purpose: Radical prostatectomy (RP) is a highly effective treatment for patients with prostate cancer. However, patients with positive surgical margins after radical prostatectomy have less than ideal outcomes with 5-year progression rates between 36% and 50%. Postoperative radiation therapy (RT) is often advocated for improving these outcomes. We identified predictors of response to adjuvant RT given for positive margins after RP. Materials and Methods: We retrospectively reviewed the clinical records of men who underwent RP between 1987 and 1999 at our institution and who received adjuvant RT for positive surgical margins. Only patients in whom prostate specific antigen (PSA) was undetectable after RP as well as before the initiation of RT were included. Numerous clinicopathological variables, including pre-RP PSA, pathological stage, margin length and location, and extracapsular extension or seminal vesicle involvement, were assessed for their adverse effect on the biochemical recurrence rate after adjuvant RT. Results: A total of 62 men met our inclusion criteria. Median age at surgery was 60.7 ± 6.1 years and median PSA at presentation was 9.0 ng/ml (range 1.4 to 64.9). The median RT dose was 60.0 ± 3.6 Gy. RT was started a median of 5.0 ± 3.6 months after RP. The 5 and 10-year biochemical disease-free survival rates for the whole group were 90.2% and 87.9%, respectively. Of all parameters tested only Gleason score 4 + 3 or greater (p = 0.037) and pre-RP PSA greater than 10.9 ng/ml (p = 0.040) were predictive of biochemical recurrence after adjuvant RT on univariate analysis. On multivariate analysis only pre-RP PSA greater than 10.9 ng/ml remained an independent predictor (p = 0.031). Conclusions: In the setting of true adjuvant RT in patients with positive margins after RP and undetectable PSA those with predominant Gleason grade 4 or greater, or PSA greater than 10.9 ng/ml at presentation are at increased risk for recurrence after adjuvant RT.