Long-term Follow-up of a Matched Cohort Study Evaluating the Role of Adjuvant Radiotherapy for Organ-confined Prostate Cancer With a Positive Surgical Margin

Objective To evaluate if adjuvant radiation therapy (ART) is associated with improved long-term oncologic outcomes for pT2N0R1 prostate cancer (PCa). Methods Men with pT2N0 PCa and a single positive surgical margin following radical prostatectomy and pelvic lymphadenectomy were identified (1987-1996). Men who received ART were matched 1:1 to men who did not receive ART based on age, year of surgery, Gleason score, preoperative prostate-specific antigen, site of positive surgical margin, and DNA ploidy. Biochemical recurrence (BCR), local recurrence, distant metastasis, and overall survival (OS) were compared between groups in time-to-event analyses. Results The cohort included 152 men (76 per group) with a median follow-up of 20 years (interquartile range 19,22). ART was associated with a lower cumulative incidence of BCR (25% vs 52%; P <.001) and local recurrence (3% vs 12%; P =.03), but no significant differences in cumulative incidence of distant metastasis (10% vs 7%; P =.44) or in probability of OS (56% vs 68%; P =.08) at 20 years. In competing risks models, receipt of ART was associated with reduced risks of BCR (hazard ratio [HR] = 0.40; 95% confidence interval [CI] 0.23-0.70; P <.001) and local recurrence (HR = 0.21; 95% CI.05-0.98; P =.05), but not distant metastasis (HR = 1.56; 95% CI 0.51-4.75; P =.43). In the Cox model, ART was not associated with improved OS (HR = 1.56; 95% CI 0.94-2.57; P =.08). Conclusion ART was associated with reduced risks of BCR and local recurrence for men with pT2N0R1 PCa. However, ART was not significantly associated with metastasis-free or OS benefits, as recurrences in these patients generally followed an indolent trajectory with 20 years of median follow-up.