Treatment Sequence In Elderly Metastatic Castration-Resistant Prostate Cancer (Mcrpc) Patients (Pts) In A Prospective Cohort Study.

5053 Background: Abiraterone (Abi), enzalutamide (Enza) and docetaxel (Doc) are all valid first-line (1L) mCRPC treatment options. SIOG guidelines (Droz, Eur Urol 2017) recommend that fit elderly pts should receive the same treatment as younger patients. Evidence of the optimal treatment sequence in this patient subpopulation is lacking. Methods: We evaluated the outcome of elderly (≥ 75 years [yrs]) pts treated in the prospective PROREPAIR-B cohort study (NCT03075735). We assessed the impact of 1L treatment option (Doc vs Abi/Enza) on overall survival (OS) and progression-free survival (PFS) to 1L-therapy following PCWG2criteria. Uni- (UV) and multivariable (MV) cox-regression models were used. MV model covariates included local therapy, Gleason Score, stage IV at diagnosis, visceral metastases, ALP (≥ULN), LDH (≥ULN), haemoglobin (Hb; ≤LNL), albumin (≤LNL) and ECOG PS. Results: 419 pts were included in the study. Of these, 137 (32,7%) had age ≥ 75 yrs. 48 (35%) received docetaxel and 88 (64.2%) had Abi/Enza as first-line therapy. Of the 121 pts that progressed on 1L-therapy, 30 (24.8%) did not receive 2L therapy. Choice of 2L-therapy was: Doc in 37 (30,6%), Abi/Enza in 38 (31.4%), Cabazitaxel in 9 (7.4%) and Radium-223 in 7 (5.8%) pts. Pts treated with 1L-Doc had higher rates of visceral metastases (22.9% vs 5.7%; p=0.003), high ALP (68.8% vs 43.2%; p=0.004) and low Hb (12.5% vs 3.4%). PFS to 1L-therapy was longer for Abi/Enza than for Doc treated pts (9.6 vs 8.3m; HR: 0.52; p=0.001). The pattern of disease progression (PSA, radiographic, clinical) was similar in Doce and Abi/Enza treated pts. No difference between pts treated with initial Abi/Enza vs Doc was observed in OS (28.2 vs 24.8m; HR:1.18; p=0.474). No significant OS differences were observed in the MV model. Conclusions: No differences in OS were observed between treatment sequences starting with Doc vs Abi/Enza in pts ≥ 75 yrs. Pts treated with 1L-Doc had worse baseline prognostic features. Age should not be considered as a factor for treatment choice in elderly mCRPC pts based on treatment outcome.