Brachytherapy boost and cancer-specific mortality in favorable high-risk and other high-risk prostate cancer.

Abstract

52 Background: A randomized trial has recently reported improved 5-year biochemical recurrence-free survival with brachytherapy (BT) boost compared with external beam radiation therapy (EBRT) boost in intermediate- to high-risk prostate cancer. Recent retrospective data suggest that BT boost may also confer a cancer-specific survival benefit in the high-risk subgroup. We sought to determine whether this survival benefit would extend to the recently defined favorable high-risk subgroup of prostate cancer patients (T1c, Gleason 4+4 = 8, PSA < 10 ng/mL or T1c, Gleason 6, PSA > 20 ng/mL). Methods: We identified 45,078 patients in the Surveillance, Epidemiology, and End Results database with cT1c-T3aN0M0 intermediate- to high-risk prostate cancer diagnosed 2004-2011 treated with EBRT or EBRT plus BT. We used multivariable competing risks regression to determine differences in the rate of prostate cancer-specific mortality (PCSM) after EBRT+BT or EBRT alone in patients with intermediate-risk, favorable high-risk, or other high-risk disease after adjusting for demographic and clinical factors. Results: BT boost was not associated with an improvement in 5-year PCSM compared with EBRT alone among patients with favorable high-risk disease (1.6% vs 1.9%; adjusted hazard ratio [AHR] 0.56; 95% confidence interval [CI], 0.21 to 1.52, P = 0.258) and intermediate-risk disease (0.7% vs 0.9%; AHR 0.83; 95% CI, 0.59 to 1.16; P = 0.270). Others with high-risk disease had significantly lower 5-year PCSM when treated with BT boost compared with EBRT alone (3.9% vs 5.0%; AHR 0.73; 95% CI, 0.55 to 0.95; P = 0.022). Conclusions: Brachytherapy boost is associated with a decreased rate of PCSM in men with high-risk prostate cancer, but this benefit was not seen among patients with favorable high-risk disease. This suggests that the recently-defined “favorable high-risk” category may be used to personalize therapy for men with high risk disease.