871PAdding ADT to PSMA-PET/CT-guided SBRT for oligometastatic prostate cancer improves distant progression-free survival

Abstract Background To report on the local response (LR), biochemical progression-free (bPFS) and distant-progression free (DPFS) survival after stereotactic body radiotherapy (SBRT) for bone and lymph node prostate cancer oligometastases. Methods Within the context of a prospective SBRT trial for oligometastases (NCT03486431), 54 bone and lymph node oligometastases, all detected on PSMA-PET/CT, were irradiated in 40 prostate cancer patients between July 2017 and December 2018. Of these patients, 35 had hormone-sensitive and 5 had castration-resistant disease. Short-term concomitant ADT was recommended in all hormone-naive patients but decided in consultation with the patient. Ultimately, 20 patients received ADT while 20 did not. The two groups were well balanced, with no significant differences in age, Gleason score, PSA, lesion type, number or timing of metastases, and fractionation schedule. All patients received a PSMA-PET/CT at 6 months after SBRT. PSMA-RADS v1.0 was used to categorize the response of the treated lesion. Quality-of-life (QOL) scoring was performed using the EORTC QLQ-C30 questionnaire at baseline, 3 and 6 months. Results Median follow-up for all patients was 9.6 months (IQR 6.3 – 12.9 months). Up till now, 42 lesions could be reevaluated at 6 months after SBRT with PSMA-PET/CT, of which 30 showed complete response, 8 partial response and 4 stable disease. No symptomatic or local progression was observed in the irradiated lesions. There was no statistically significant influence of ADT, fractionation, type of lesion or lesion size on LR. Patients who received ADT had significantly improved bPFS (median bPFS of 6.9 months versus median not reached; p = 0.0017) and DPFS (median DPFS of 6.8 months versus 17.3 months; p = 0.0021). We did not observe any clinically relevant changes in QOL scores between the patients who received ADT versus those who refused. Overall, QOL scores remained stable for both groups at baseline, 3 and 6 months. Conclusions These prospective data, although non-randomized, suggest that oligometastatic prostate cancer patients treated with SBRT could potentially benefit from short-term ADT. Longer follow-up will determine if ADT simply delays progression or truly alters the course of the disease. Clinical trial identification NCT03486431. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.