Real‐world outcomes in patients with hormone receptor positive, human epidermal growth factor receptor 2 receptor‐negative advanced breast cancer and visceral metastases at baseline – advanced hormone receptor positive breast cancer registry in Australia

Background Hormone receptor‐positive, HER2− breast cancer (HR+/HER2−) represents most advanced breast cancer (ABC) cases. Patients with visceral metastases are considered to have aggressive disease, historically treated with first‐line chemotherapy (CT). However, trials (RIGHT Choice, PADMA, ABIGAIL) have demonstrated that cyclin‐dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) provide superior efficacy and tolerability in this setting. Aims To compare outcomes between first‐line CDK4/6i + ET and CT in Australian patients with HR+/HER2− ABC and visceral metastases. Methods Data were obtained from the ARORA registry, a prospective observational study capturing real‐world outcomes for Australian patients with HR+/HER2− ABC. Eligible patients were aged ≥18 years, with visceral metastases diagnosed after 1 January 2020, and received first‐line systemic therapy. Participants were stratified by initial treatment: CT, ET + CDK4/6i or ET monotherapy. ET monotherapy was analysed as a separate cohort and excluded from comparative progression‐free survival (PFS) and overall survival (OS) analyses. Primary endpoints were (1) OS: time from metastatic diagnosis to death and (2) PFS: time to progression on first‐line therapy. Results A total of 418 patients were included, with a median age of 56 years and median follow‐up of 12 months. The majority of patients (73.7%) received first‐line CDK4/6i + ET. Compared with CT, CDK4/6i + ET yielded significantly longer PFS (20.0 vs 11.9 months, P = 0.0006). A trend towards improved OS was observed (28.6 vs 22.9 months, P = 0.1399). Conclusion This real‐world analysis reinforces CDK4/6i + ET as the preferred first‐line treatment for HR+/HER2− ABC with visceral metastases. While selection bias cannot be excluded, these findings support the shift away from routine first‐line CT. Ongoing follow‐up will clarify the OS impact.