Paul L. Nguyen, MD, Dana-Farber Cancer Institute, Boston, MA, shares the results of the Phase II randomized FORMULA-509 (NCT03141671) trial assessing post-operative salvage radiotherapy and 6 months of GnRH agonist with or without abiraterone acetate/prednisone and apalutamide post-radical prostatectomy in patients with a rising PSA after radical prostatectomy. The primary endpoint was PSA progression-free survival (PFS) and secondary endpoint was metastasis-free survival (MFS) determined by conventional imaging. 345 participants (332 evaluable) from 9 sites were randomized (172 bicalutamide, 173 abiraterone acetate/prednisone and apalutamide). Median follow-up was 34 (6-53) months; 29% were pN1 and 31% had PSA more than 0.5 ng/mL. The HR for PFS was 0.71 and the HR for MFS was 0.57. In a pre-planned analysis by stratification factors, acetate/prednisone and apalutamide was significantly superior for patients with a PSA level more than 0.5 and for MFS. No statistically significant benefit was detected in pre-planned analyses of stratification subgroups defined by PSA≤0.5, pN0, or pN1. Adverse events were consistent with the known safety profiles of the agents being studied. Although this primary analysis did not meet the pre-specified threshold for statistical significance, it strongly suggests that the addition of abiraterone acetate/prednisone and apalutamide to salvage radiation plus 6 months of ADT may improve PFS and MFS, particularly in the subgroup of patients with a PSA level over 0.5. This interview took place at the ASCO GU Cancers Symposium 2023 in San Francisco, CA.
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