Meta-analysis finds oral SERDs improve PFS over standard ET in HR+ HER2- ABC

PURPOSE: The development of endocrine resistance is frequent in hormone receptor-positive, HER2-negative advanced breast cancer (HR + /HER2-ABC), particularly after CDK4/6 inhibitor exposure. Next-generation oral selective estrogen receptor degraders (SERDs) have been developed to improve estrogen receptor blockade; however, randomized trials have yielded heterogeneous results with uncertain clinical benefit. METHODS: A PRISMA 2020 compliant systematic review and meta-analysis with PROSPERO registration was conducted. PubMed, Embase, and Cochrane CENTRAL were searched through October 2025 for phase II-III randomized trials comparing oral SERDs with standard endocrine therapy (ET) in HR + /HER2-ABC after prior ET. The primary endpoint was progression-free survival (PFS); secondary endpoints included overall survival (OS), objective response rate (ORR), and treatment-related adverse events (TRAEs). Treatment effects were pooled using random effects models with prespecified subgroup analyses by ESR1 mutation status and key clinical characteristics. RESULTS: Six randomized trials, including 2808 patients, were analyzed. Oral SERDs improved PFS versus standard ET in the overall population (hazard ratio [HR] 0.79; 95% confidence interval [CI] 0.70 to 0.89). ORR was higher with oral SERDs (odds ratio [OR] 1.67; 95% CI 1.23 to 2.28), corresponding to absolute response rates of approximately 21% versus 14%. An OS improvement was observed (HR 0.72; 95% CI 0.57 to 0.90), although follow-up was limited. Benefit was concentrated in ESR1-mutated tumors (PFS, HR 0.57; 95% CI 0.48 to 0.67) with no significant PFS advantage in ESR1 wild-type disease. Gastrointestinal adverse events were more frequent with oral SERDs compared with the control ET. CONCLUSIONS: Pooled randomized evidence supports a clinically meaningful benefit of oral SERDs over standard ET after endocrine progression in HR + /HER2-ABC, with the strongest and most consistent efficacy observed in ESR1-mutated disease.