Brachytherapy monotherapy may be sufficient for a subset of patients with unfavorable intermediate risk prostate cancer

Purpose/objective(s): Brachytherapy (BT) monotherapy is a well-established treatment modality for favorable intermediate risk (FIR) prostate cancer. However, patients with unfavorable intermediate risk (UIR) disease are often recommended trimodality therapy involving BT, androgen deprivation therapy (ADT), and external beam radiation therapy (EBRT). We sought to investigate the relative benefit of supplemental therapies (ADT and/or EBRT) for FIR and UIR prostate cancer in a large dataset.

Materials/methods: We identified 3,723 patients with intermediate risk prostate cancer treated with BT between 1997 and 2013, including 1,989 and 1,734 patients with FIR and UIR disease, respectively. For the FIR cohort, Fine and Gray's competing risks regression model was used to evaluate whether there was a difference in prostate cancer specific mortality (PCSM) between BT vs. BT + supplemental therapy (ADT, EBRT, or both). For the UIR cohort, this regression model was used to evaluate whether supplemental ADT, EBRT, or both decreased PCSM beyond BT alone. Both regression models were adjusted for clinical and treatment-related factors.

Results: The median follow-up periods were 7.7 years (interquartile range: 5.4-10.5) for the FIR cohort and 7.8 years (interquartile range: 5.3-10.6) for the UIR cohort. For the FIR cohort, there was no difference in PCSM between BT monotherapy vs. BT + supplemental therapy (adjusted hazard ratio [AHR] = 1.70; 95% CI: 0.46-6.29; P = 0.43). For the UIR cohort, supplemental EBRT (AHR = 2.66; 95% CI: 1.12-6.34; P = 0.03), ADT (AHR = 0.96; 95% CI: 0.38-2.43; P = 0.93), or both (AHR = 1.46; 95% CI: 0.42-5.01; P = 0.55) were not associated with improved PCSM compared with BT alone.

Conclusion: In our analysis, supplemental therapies did not offer an improvement in PCSM compared with BT alone for FIR or UIR prostate cancers. Further prospective clinical trials are required to determine whether BT monotherapy may be sufficient for a subset of patients with UIR disease.