LDR-Brachytherapy monotherapy appears unsuited for NCCN unfavorable intermediate-risk prostate cancer patients

Background: To validate the subdivision of intermediate-risk (IR) prostate cancer (PCa) into favorable intermediate-risk (FIR) and unfavorable intermediate-risk (UIR) PCa in a historical patient cohort and to compare 2 different radiotherapy regimens. Methods: Patients with intermediate-risk (IR) PCa, treated either by ¹²⁵J-LDR-brachytherapy monotherapy (BT) or by combined-modality radiation therapy (CRT), were retrospectively subclassified into FIR and UIR and reanalyzed with regard to biochemical recurrence-free survival (BRFS), metastasis-free survival (MFS), and prostate cancer-specific survival (CSS). Kaplan-Meier product-limit method and log-rank tests were applied to estimate survival probabilities and compare survival, respectively. Uni- and multivariable analyses were performed using Cox proportional hazard regression. Results: Of 490 IR patients, 252 had received BT (86.5% FIR, 13.5% UIR), and 238 had received CRT (30% FIR, 70% UIR). Retrospective analysis revealed that BRFS at 10 years was 81% for BT, and 94% for CRT in FIR patients. For UIR patients, BRFS at 10 years was 37% for BT, and 89% for CRT. MFS at 10 years for FIR patients was 87% for BT, and 94% for CRT. For UIR patients MFS at 10 years was 78% for BT, and 95% for CRT. In multivariable analysis treatment (BT vs. CRT) was the single associated factor for biochemical recurrence, and for metastases in the UIR group (BFRS, P < 0.001, HR 16.07 (CI 4.23–61.10); MFS, P = 0.011, HR 8.43 (CI 1.62–43.9). Conclusions: Subclassification of IR prostate cancer into FIR and UIR subcategories appears mandatory. For FIR patients, outcomes after BT monotherapy were acceptable. However, clinical failure after ¹²⁵J-LDR-BT in UIR patients was notably increased, suggesting that BT monotherapy was less successful in this risk group. In contrast, the outcome in UIR patients after CRT was excellent.