The efficacy of metastasis-directed external beam radiotherapy for castration-resistant prostate cancer: A retrospective multicenter study.

Background: To assess the efficacy of metastasis-directed external beam radiotherapy (MDT) in patients with castration-resistant prostate cancer (CRPC), we conducted a multicenter retrospective study.

Materials and methods: We retrospectively analyzed data from patients with metastatic CRPC treated with MDT between January 2013 and July 2023 across 14 hospitals. Patients who received palliative or local radiation therapy or had insufficient clinical data were excluded. The primary endpoint was the change in prostate-specific antigen (PSA) levels from pre- to post-MDT. Secondary endpoints included overall survival, time to next systemic therapy, PSA progression-free survival, and reduction of target lesions assessed radiographically.

Results: Among 579 patients with metastatic prostate cancer who received radiation therapy, 48 underwent MDT. The median follow-up period was 325 days, and the median patient age was 74 years. Metastasis-directed external beam radiotherapy target sites included bone (n = 34, 70.8%), lymph nodes (n = 11, 22.9%), local recurrence (n = 2, 4.2%), and other sites (n = 1, 2.1%). Of the 48 patients, 30 (62.5%) showed a decrease in PSA levels after MDT, and 20 (41.6%) achieved a PSA reduction greater than 50%. Among the 26 patients who underwent post-MDT radiographic evaluation, 11 (42.3%) demonstrated a reduction in target lesions. Median overall survival, PSA progression-free survival, and time to next systemic therapy for patients with and without a PSA response were 1307 versus 614 days (p = 0.038, log-rank test), 233 versus 98 days (p = 0.014, log-rank test), and 434 versus 450 days (p = 0.273, log-rank test), respectively. The median PSA doubling time was 4.1 months in PSA responders and 1.7 months in nonresponders.

Conclusions: Metastasis-directed external beam radiotherapy resulted in PSA reduction in 62.5% of patients with metastatic CRPC. Metastasis-directed external beam radiotherapy may be a suitable treatment option for patients with a favorable prognosis but may not benefit those with a poor prognosis and short PSA doubling time.