Clinical Outcomes of Combined Prostate- and Metastasis-Directed Radiation Therapy for the Treatment of De Novo Oligometastatic Prostate Cancer.

PURPOSE

The Systemic Therapy in Advancing or Metastatic Prostate Cancer: Evaluation of Drug Efficacy (STAMPEDE) trial reported overall survival benefits for prostate-directed radiation therapy (PDRT) in low-burden metastatic prostate cancer. Oligometastasis-directed radiation therapy (ORT) improves androgen deprivation therapy (ADT)-free and progression-free survivals. Comprehensive PDRT + ORT to all detectable metastases may offer benefit for de novo oligometastatic prostate cancer (DNOPC) and is under prospective study; given few available benchmarks, we reviewed our institutional experience.

METHODS AND MATERIALS

Forty-seven patients with DNOPC with predominantly M1b disease received neoadjuvant, concurrent, and adjuvant ADT plus PDRT + ORT to 1 to 6 oligometastases. Gross pelvic (N1) nodes were not considered oligometastases unless focally targeted without broader nodal coverage. Outcomes were analyzed from radiation therapy (RT) start using Kaplan-Meier, competing risks, and Cox regression. Median follow-up was 27 (95% confidence interval, 16-42) months.

RESULTS

At 1- and 2-years post-RT, cumulative incidence of distant metastatic progression (DMP) was 21% and 32%, whereas overall survival was 90% and 87%, respectively. Neuroendocrine/intraductal histology, prostate-specific antigen (PSA) < 20, and detectable PSA after PDRT + ORT were associated with increased DMP risk; number and location of oligometastases were not. Local failure was rare, with 3 prostate recurrences and progression of 10 treated oligometastases during follow-up. After neoadjuvant ADT, 9 (19%) patients had undetectable PSA (<0.05 ng/mL), which increased to 32 (68%) after PDRT + ORT. Overall 2-year incidence of biochemical recurrence (BCR) and development of castrate resistance were 23% and 36%, respectively. Undetectable PSA post-RT was associated with lower risk of BCR (hazard ratio, 0.19; = .004) and DMP (hazard ratio, 0.26; = .025). Overall, 23 (49%) patients were trialed off ADT; 16 (70%) had testosterone recovery (>150 ng/dL) and, of these, 5 had subsequent PSA rise and restarted ADT 2 to 21 months postrecovery. The remaining 11 were maintained off ADT without BCR. Median noncastrate duration was 8 months; 7 patients had normalized testosterone for >1 year.

CONCLUSIONS

A comprehensive, radiotherapeutic-based treatment strategy has favorable clinical outcomes and can produce prolonged noncastrate remissions in a subset with DNOPC.