Activity of fulvestrant in HER2-overexpressing advanced breast cancer

Background: Human epidermal growth factor receptor 2 (HER2) overexpression increases the aggressiveness of breast cancer cells resulting in poorer prognosis. Patients with HER2-positive disease are less responsive to endocrine therapies. Trastuzumab monotherapy results in objective responses in only similar to 15% of patients. Fulvestrant retains activity in cells overexpressing HER2 that are resistant to other endocrine treatments. This retrospective study evaluated response to fulvestrant treatment among HER2-positive patients with advanced breast cancer (ABC). Patients and methods: Clinical experience data from 10 treatment centres were pooled. Postmenopausal patients with predominantly hormone receptor-positive and HER2-positive disease were included. Clinical benefit (CB) was defined as the proportion of patients achieving a response to treatment (partial or complete) or stable disease lasting 6 months. Results: Data for 102 patients were analysed. Fulvestrant resulted in an overall CB rate of 42% (43/101) in HER2-positive patients and 40% (25/63) in patients with visceral disease. Median duration of treatment was 14.5 months (range 6-44 months). Fulvestrant showed activity up to the fourth line of endocrine therapy and up to the seventh line of overall therapy. Conclusions: Results indicate that fulvestrant may be a suitable treatment option in extensively pre-treated patients with HER2-positive, hormone receptor-positive ABC. Further exploration of its use in this patient population is warranted.