Long-term outcomes of combining prostate brachytherapy and metastasis-directed radiotherapy in newly diagnosed oligometastatic prostate cancer: A retrospective cohort study

BackgroundSystemic Therapy in Advancing or Metastatic Prostate Cancer: Evaluation of Drug Efficacy (STAMPEDE) trial showed the survival benefit for prostate radiotherapy in newly diagnosed prostate cancer patients with a low metastatic burden. The result raises the next question whether additional radiotherapy to metastatic sites could improve the survival in those with a low metastatic burden. MethodsWe evaluated the efficacy and safety of prostate-directed radiotherapy (PDRT) with or without metastasis-directed radiotherapy (MDRT) in newly diagnosed oligometastatic patients who underwent combination of high-dose-rate prostate brachytherapy, external beam radiotherapy, and androgen deprivation therapy. Forty patients with bone metastasis and node positive prostate cancer were retrospectively analyzed. Of these, 22 (55%), 3 (7%), and 15 (38%) patients had N1M0, M1a, and M1b, respectively. Eighteen patients (45%) received MDRT to all metastatic sites. All patients initially underwent 6 months of androgen deprivation therapy. Oligometastatic disease was defined as presence of five or fewer metastatic lesions. Median follow-up period was 62.5 months. ResultsOf the 40 patients, the 5-year castration-resistant prostate cancer (CRPC)-free survival rate and cancer-specific survival was 64.4% and 87.9%, respectively. Pre- or post-treatment predictive value including prostate-specific antigen (PSA) at diagnosis 20ng/mL, Gleason grade group 5, positive biopsy core rate 51%, PSA nadir level of 0.02ng/mL after the radiotherapy, and no MDRT were significantly associated with progression to CRPC. Patients with MDRT had significantly higher probability of achieving a PSA level of <0.02ng/mL than those without the therapy (88.8% vs 54.5%, P=0.0354) and consequently had a better CRPC-free survival than those without the therapy (HR 0.319, 95%CI: 0.116-0.877). Comparing PDRT alone, PDRT with MDRT did not significantly increase the incidences of genitourinary and gastrointestinal toxicities. ConclusionsThis single-institutional study revealed the feasibility of combining prostate brachytherapy and MDRT for newly diagnosed oligometastatic prostate cancer. This combined approach has potential to prolong CRPC-free survival.