Complete response to pyrotinib combined with letrozole as first-line treatment of HER2-positive/HR-positive breast cancer: a case report

Approximately 15–20% of breast cancer patients are epidermal growth factor receptor 2 (HER2)-positive, and about half of these are also hormone receptor (HR)-positive. The mainstay treatment for HER2-positive/HR-positive patients is anti-HER2 treatment combined with chemotherapy. However, many patients are not suitable for this treatment regimen due to their poor physical health and inability to tolerate chemotherapy. Pyrotinib is a novel, irreversible tyrosine kinase inhibitor (TKI) with activity against EGFR/HER1, HER2, and HER4. Several studies have shown pyrotinib’s anti-tumor activity and safety profile in treating HER-2 positive breast cancer patients, but its effect on metastatic breast cancer (MBC) when combined with letrozole as a first-line treatment remains to be verified. Here, we present a case of a 50-year-old postmenopausal HER2-positive/HR-positive breast cancer patient who received pyrotinib plus letrozole as a first-line treatment following a diagnosis of left axillary lymph node and double lung metastases after modified radical mastectomy for left breast cancer. Two months after administration of combined pyrotinib and letrozole, a complete response (CR) was confirmed by CT scan. The patient experienced only mild and tolerable adverse events. At the time of writing, the patient was still alive without any recurrence. Our case indicates that the combined therapy of pyrotinib plus letrozole may/can be a promising treatment option for patients with HER2-positive/HR-positive MBC. Nevertheless, further evidence is needed to verify this conclusion.