The successful application of pyrotinib in the treatment of primary trastuzumab-resistant HER-2-positive breast cancer with bilateral axillary lymph node metastasis: a case report.

Breast cancer patients with synchronous contralateral axillary lymph node metastasis (CAM) are very rare, and there is a lack of published treatment guidelines for this kind of patients. We presented a human epidermal growth factor receptor 2 (HER-2)-positive breast cancer case, who was diagnosed as CAM with primary trastuzumab resistance. In this case report, we describes a 47-year-old woman diagnosed with HER-2 positive breast cancer with regional lymph nodes metastasis. However, physical examination identified contralateral axillary lymph nodes, the auxiliary inspection did not assist in determining the nature of the right axillary lymph nodes, and there was no obvious mass in the right breast. Hence, we performed the core needle biopsy on the right axillary lymph node, which revealed the presence of metastatic breast adenocarcinoma. The patient received trastuzumab-based treatment, but this only afforded a progression-free survival of 5 months, owing to primary trastuzumab resistance. She was then successfully treated with pyrotinib, and the outcome was close to clinical complete response (CCR) with a progression-free survival of over 27 months thus far. This case report may help inform clinicians in the diagnosis of breast cancer with CAM and offer the treatment options in HER-2-positive metastasis breast cancer with primary trastuzumab resistance.