Fulvestrant and trastuzumab in patients with luminal HER2-positive advanced breast cancer (ABC): an Italian real-world experience (HERMIONE 9)

Purpose The most appropriate therapy for HR+/HER2-positive (HER2+) advanced breast cancer (ABC) is a matter of debate. Co-targeting of both receptors represents an attractive strategy to overcome the cross-talk between them. Methods The HERMIONE 9 is an observational retrospective multicentric study which aimed to describe the clinical outcome of patients with HR+/HER2+ABC who received the combination of Fulvestrant (F) and Trastuzumab (T) as part of their routine treatment at 10 Italian Institutions. Results Eighty-seven patients were included. Median age was 63 (range, 35–87) years. The median number of previous treatments was 3 (range, 0–10) and F and T were administered as≥3rd line in 67 patients. Among the 86 evaluable patients, 6 (6.9%) achieved CR, 18 (20.7%) PR, and 44 (50.6%) had SD ≥24 weeks with an overall CBR of 78.2%. At a median follow-up of 33.6 months, mPFS of the entire cohort was 12.9 months (range, 2.47–128.67). No diference was observed in mPFS between patients treated after progression or as maintenance therapy (mPFS 12.9 and 13.9 months in 64 and 23 patients, respectively), neither considering the number of previous treatment lines (≤3 or<3). Conclusion The combination of F and T was active in this cohort at poor prognosis and deserves further investigations possibly in combination with pertuzumab in patients with high ER expression.