Impact of stereotactic body radiotherapy after progression in castrate resistant prostate cancer patients undergoing first line abiraterone treatment. A subgroup analysis from ARTO trial (NCT03449719).

Background: ARTO trial was a phase II randomized trial suggesting the benefit of a concomitant treatment strategy including Abiraterone acetate plus predisone (AAP) and stereotactic body radiotherapy (SBRT) in oligometastatic castrate resistant prostate cancer (omCRPC). The object of the current analysis is to explore whether the benefit provided by SBRT to AAP is maintained at later stages of disease after oligoprogression METHODS: Patients enrolled in ARTO trial in whom a first progression event was reported were divided in two groups according to the treatment approach received, regardless of the initial randomization. After first progression event, Patients in Group A received SBRT on oligoprogressive disease, while patients in group B received second line systemic treatment. Palliative RT was not considered for the purpose of this analysis. Progression-Free survival (PFS) 1 and 2 were defined as time between AAP start and first progression event and time between first and second progression event, death or last follow up, (whichever came first), respectively. Cox regression analysis was performed to compare PFS1 + PFS2 in patients in group A vs Group B. Kaplan-Meier analysis was performed to compare overall survival between the two groups RESULTS: Median PFS1 + PFS2 was 45.9 months vs. not reached in group A (n = 43) vs Group B (n = 20), respectively (HR 0.63, 95% CI 0.17-2.33, p value 0.489), no significant difference was detected. Median OS was not reached in neither of the two arms of treatment, with a non-significant trend in favour of the experimental arm (HR 0.50, 95% CI 0.14-1.78, p = 0.284) CONCLUSIONS: Results from the present analysis show that SBRT after progression may be a viable and feasible option for omCRPC after progression if compared to second line systemic therapy.