Significant response to the combination of pyrotinib and letrozole in a patient with metastatic HER2-positive and hormone receptor-positive breast cancer: a case report

Breast cancer is the most commonly diagnosed malignant tumor and the leading cause of cancer-related death in women worldwide. Previous studies have demonstrated that patients with human epidermal growth factor receptor 2 (HER2)-positive/hormone receptor (HR)-positive metastatic breast cancer can benefit from HER2-targeted therapy. Pyrotinib, an irreversible tyrosine kinase inhibitor (TKI), has been demonstrated to be effective and safe in treating HER2-positive breast cancer patients. Letrozole is an aromatase inhibitor (AI) which has shown better clinical efficacy when combined with HER2 inhibitors in treating patients with HER2-positive and HR-positive breast cancer than has hormonal therapy alone. However, the effect of combination therapy with pyrotinib plus letrozole in HER2-positive/HR-positive metastatic breast cancer patients has not yet been investigated. In this case report, a 57-year-old female patient with HER2-positive/HR-positive breast cancer received modified radical mastectomy and experienced subsequent relapse and metastasis. She was diagnosed with relapsed right breast cancer, a right chest bone mass accompanied by bone destruction, and metastases in the chest wall and both lungs. She was then enrolled in a phase II clinical trial and was treated with pyrotinib plus letrozole, and achieved a durable clinical response. Our case shows that combination therapy with pyrotinib plus letrozole may provide significant clinical benefit for patients with HER2-positive/HR-positive metastatic breast cancer, with tolerable adverse events.