The HERMOINE 9 trial was an Italian observational, retrospective multicenter study intended to describe the clinical outcome of patients with HR+/HER2+ ABC patients who received as part of their routine treatment the combination of fulvestrant, an estrogen-receptor antagonist, and trastuzumab, an anti-HER2 monoclonal antibody.

Women aged >18 years with HR+ (defined as estrogen receptor [ER] and/or progesterone receptor [PR] >10%) and  + inoperable locally advanced and/or metastatic BC were eligible for enrollment in the study. Premenopausal women were also given concomitant ovarian suppression with GnRH analogues.

Fulvestrant 500 mg IM was administered every 28 days with a loading dose after 14 days. The dose of trastuzumab was either an 8-mg/kg loading dose followed by a 6 mg/kg IV infusion or a 600-mg SC dose every 21 days. (In the United States, the approved dose of fulvestrant monotherapy or for combination with palbociclib, abemaciclib, or ribociclib is 500 mg IM as two 5-mL injections, one in each buttock, on Days 1, 15, and 29, and once monthly thereafter.)

Treatment response was classified as complete response (CR), partial response (PR), stable disease (SD), or progressive disease (PD). Clinical Benefit Rate (CBR) was the percentage of patients who achieved CR, PR, and SD at >24 weeks. Progression-free survival (PFS) was the time from the first day of fulvestrant + trastuzumab until disease progression via radiological or clinical examination or death from any cause. Time to progression (TTP) was also assessed.

A total of 87 women with a median age of 63 years were enrolled in the study; 28% were premenopausal. Of these patients, 31% were diagnosed with de novo metastatic BC and 69% with recurrent disease. The median time to recurrent disease was 57.1 months.

Of the primary tumors, 67.8% were triple positive (ER+, PR+ and HER2+), but only 49% of metastatic tumors were positive for all three receptors. Over three-quarters of patients received fulvestrant and trastuzumab as third-line therapy.

Twenty-six percent of patients received fulvestrant and trastuzumab as maintenance therapy. The other approximate three-quarters of patients had progressed on their previous regimen, which had consisted of endocrine therapy with trastuzumab, anti-HERs therapy with chemotherapy, or chemotherapy alone.

The median duration of fulvestrant and trastuzumab treatment was 11.5 months. Of the 87 patients, response to treatment was available for 86 women. Response consisted of 6.9% CR, 20.7% PR, and 58.6% SD, with over half of patients with SD lasting 6 months of longer. The CBR was 78.2%.

The median PFS was 12.9 months after a median follow-up period of 33.6 months. The TTP was shorter during the treatment period immediately preceding fulvestrant and trastuzumab. There was no difference in median PFS based on whether patients were treated after progression to a previous line of treatment, if they were on maintenance therapy, if they had received fewer than three or more than three lines of treatment, whether they received chemotherapy or endocrine therapy, or if they had triple-positive BC or single HR expression.  

Although further study is needed, this study provides pharmacists with useful, real-world information about the use of fulvestrant and trazutumab for women with triple-positive ABC.

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