A disease registry study to prospectively observe treatment patterns and outcomes in patients with HER2+unresectable locally advanced or metastatic breast cancer (aBC): Interim results of the ESTHER study (NCT02393924)

Background: Over the last decade the standard-of-care treatment for patients with HER2+ aBC has included anti-HER2 therapies often combined with chemotherapy. These approaches have shown efficacy in clinical trials which have recruited patients in restricted populations defined by lines of therapy and previous treatments. There are few data regarding the long-term outcomes of patients treated with these regimens, including those with brain metastases. We conducted a prospective, multicentre non-interventional study to observe anti-cancer treatment regimens and clinical outcomes in patients with HER2 positive aBC.

Methods: Adult patients diagnosed with HER2-positive aBC within the last 6 months were included. No specific treatment approach or course was mandated by the protocol. Source data was taken from the patient’s chart and other medical records, then reported by means of an electronic data collection system. Data regarding treatment received, efficacy (progression-free and overall survival (PFS), response rates (RR) and development of CNS metastases) and safety (including cardiac toxicity) were captured.

Results: Between February 2015 and April 2018, 311 eligible patients were recruited with median age 57 years (24-96). At diagnosis of aBC the most common distant metastatic sites were bone (n = 145;47%), liver (n=117;38%), lung (n=100;32%) and brain (n=21;7%). First line treatment was with pertuzumab (P)/trastuzumab(T)/chemotherapy (n=212;68%), T/chemotherapy (n=45;14%), other T combinations without P (n=19;6%), Trastuzumab Emtansine regimens without T or P (n=16;5%) (19; 5% other combinations). Patients’ status as of cut-off date for this analysis (28th Feb 2022, median follow-up 44.1 months) is shown. The median PFS of patients treated in the 1st, 2nd and 3rd lines was 26.7 months, 10.7 months and 8.6 months. At the time of this analysis an additional 60 patients (19%) had developed brain metastases during first line. The number of patients starting 2nd, 3rd and 4th line treatment with brain metastases were 28 (22%), 17 (40%), 7 (37%) respectively.

Conclusions: In routine clinical practice, as reflected by this registry, at least 40% of patients who initiate first line therapy for advanced breast cancer do not proceed to 3rd line therapy, and brain metastases become increasingly common. These findings have implications for selection of optimal 2nd and 3rd line treatment. Clinical trial information: ISRCTN02393924.