Real-world assessment of AR-LBD mutations in metastatic castration-resistant prostate cancer.

Abstract

204 Background: Treatment of men with metastatic castration-resistant prostate cancer (mCRPC) using drugs targeting the AR pathway is hampered by development of resistance including activating AR ligand-binding domain (LBD) point mutations. AR LBD mutations are found in approximately 10-20% of patients (pts) with mCRPC progressing on AR pathway inhibition (ARPi) therapy and may be associated with AR activation by alternative steroid hormones. We utilized the Guardant INFORM real-world database to explore the detection rate and clinical features associated with AR-LBD mutations in men with mCRPC. Methods: This observational study was conducted in a nationally representative clinical-genomic database of 200,000+ advanced cancer pts undergoing comprehensive ctDNA analysis (Guardant360, Redwood City, CA) between 2014 and 2021, with associated clinical information from administrative claims. ctDNA samples of men with mCRPC were assessed for presence or absence of an activating AR-LBD mutation. The incidence of co-occurring genetic alterations was also investigated. Clinical outcomes were studied for matched cohorts comparing pts following first line (1L) or second line (2L) mCRPC therapy with or without AR-LBD mutations. Results: Of 15,705 prostate cancer pts included in the database, 8420 (53.6%) had mCRPC at the time of sample collection. 4122 (49.0%) of these mCRPC pts had prior treatment with an ARPi, of which 854 (21%) had an AR-LBD mutation. AR-LBD mutation prevalence was 15% in mCRPC pts untreated with an ARPi, 23% in those after 1 line, and 24% in those after 2 lines of ARPi treatment. AR L702H and T878A/S showed the greatest increase in prevalence post abiraterone, whereas AR L702H, T878S and F877L had the greatest increase in prevalence post enzalutamide. Prevalence of AR L702H and H875Y doubled (from 8.8% to 17.5%) for pts that received chemotherapy post ARPi, while AR F877L incidence declined by half (3.5% to 1.7%). Compared to pts without AR-LBD mutations, AR-LBD+ mCRPC pts were enriched for co-alterations in APC, CTNNB1, PTEN, BRCA2, and ARID1A. Rates of TP53 and RB1 alterations were comparable in the AR-LBD+ and ARLBD- cohorts. Matched mCRPC pts had similar time-to-treatment-discontinuation (TTD) and time-to-next-treatment (TTNT) between AR-LBD+ and AR-LBD- mCRPC pts in the 1L and 2L settings; however, AR-LBD+ pts exhibited worse overall survival from 1L mCRPC therapy (50.1 vs 60.7 months, log-rank P=0.013). Conclusions: In this large database, the overall detection rate of activating AR-LBD mutations in men with mCRPC undergoing ctDNA analysis was 21%, and increased with prior use of 2nd generation ARPi (abiraterone and enzalutamide). Men with AR-LBD mutations were more likely to harbor other alterations relevant to tumor progression. These findings inform on the ctDNA prevalence and impact of AR-LBD mutations in a real-world dataset of mCRPC.