Purpose: The treatment strategy for hormone receptor-positive (ER+) HER2-positive (HER2+) metastatic breast cancer has been modified since several randomized trials have proven the effectiveness of anti-HER2 targeted therapy. Previously validated clinical practice guidelines recommending the use of endocrine therapy alone in first line might be changed.
Methods: This study focused on the outcomes of women with ER+ HER2+ metastatic breast cancer receiving first-line endocrine therapy alone at the Léon-Bérard Centre, Lyon, France.
Results: Of 290 patients with ER+ HER2+ tumors, 32 (11%) met the criteria for inclusion. The median age was 54 years (29-79 years). Eighteen patients (56%) had only bone and/or soft tissue metastases. Most patients (n = 21; 65%) had only one metastatic site. Fifteen (47%) had histological grade III disease. The median progression free survival (PFS) was 8.2 months (95% CI: 0.1-16.3) and the median overall survival (OS) was 48 months (95% CI: 22.9-72.9). The overall response rate was 25% (95% CI: 11-49%), including one patient with complete response and seven with partial responses. Ten patients (31%) had stable disease. After failure of endocrine therapy, all patients received trastuzumab. The median PFS after first-line chemotherapy was 8.4 months (95% CI: 5.1-11.8). We identified a group of 10 patients with good prognostic factor (tumor grade < 3 tumors and no visceral metastases), for whom median PFS was 15.5 months (95% CI: 7-23).
Conclusions: Our result suggests that first-line endocrine therapy is a viable therapeutic option for a selected population of metastatic breast cancer patients with HER2-positive tumors. Genomic and transcriptomic signature could help to identify tumors that remain dependant of estrogen-signaling pathway.