Efficacy of Dual Hormonal Therapy with Fulvestrant and Aromatase Inhibitors as Neoadjuvant Endocrine Treatment for Locally Advanced Breast Cancer

Abstract

Background: The role of neoadjuvant endocrine therapy (NET) in patients with luminal tumors is still not well defined in everyday clinical practice. To assess the efficacy of combination NET, we analyzed the outcomes of fulvestrant and aromatase inhibitors (AI) in combination in a real-world population. Methods: This was a single-arm, retrospective longitudinal study of the total population of patients diagnosed with locoregionally advanced, clinical stage II-III, HR+ HER2-, luminal-type eBC, who were treated with the neoadjuvant combination of fulvestrant and AI between 2019 and 2024 at the Clinical University Hospital of Split, Croatia. Results: We enrolled 44 patients in the intention-to-treat (ITT) population, while 34 completed NET and surgery (per-protocol population; PPP). The median duration of NET was 11 months (interquartile range [IQR] of 9-16 months). The best radiological objective response rate (partial or complete response) was achieved by 30 (68.2%) in ITT, and 26 (76.5%) in PPP, defined by radiological examination, breast ultrasound, or MR. In the PPP, the minimal or moderate pathological response according to residual cancer burden (I or II) was observed in 29 (85.3%) patients. The median of absolute changes in Ki-67 was -5 (95% CI: -9 to 0), and the median of relative Ki67 changes was -40% (95% CI: -72% to 0%). Post-surgical Ki-67 was significantly predicted by initial Ki-67, positive lymph nodes, and time from diagnosis to the initiation of NET. Treatment was well tolerated, with no therapy discontinuation or dose reductions needed due to toxicity. The most commonly reported side effects included musculoskeletal pain (45.5%), asthenia (34.1%), and hot flashes (29.5%). Conclusions: Dual hormonal therapy with fulvestrant and AI is an active, easily given, non-toxic, promising neoadjuvant treatment in real-world patients with locally advanced luminal-type eBC who are not candidates for chemotherapy.

Keywords: Ki-67 antigen; aromatase inhibitors; breast neoplasms; endocrine therapy; fulvestrant; neoadjuvant therapy; real-world evidence.