Significant response to margetuximab in Chinese HER2-positive metastatic breast cancer patient who progressed after second-line targeted therapy.

Activation of the antibody-dependent cellular cytotoxicity is one of the key mechanisms of anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody treatment. Margetuximab is a fragment C (Fc)-modified chimeric anti-HER2 immunoglobulin G1 monoclonal antibody that shares epitope specificity with trastuzumab. In this case, we reported that margetuximab plus chemotherapy was effective as later-line therapy in a postmenopausal Chinese woman with metastatic diseases, who was diagnosed with estrogen receptor -, progesterone receptor (PR)-, HER2+ invasive ductal carcinoma. This patient used paclitaxel-albumin plus trastuzumab and pertuzumab as the first-line therapy with progression-free survival (PFS) of 14 months, and pyrotinib in combined with vinorelbine as the second-line therapy with a PFS of 17 months. Then she received margetuximab plus capecitabine as the third-line treatment, the metastatic lesions in the liver were obviously shrunk, indicating clinical partial response and the PFS was 7 months. This case revealed that margetuximab plus chemotherapy may be an appropriate option for the patients who progressed after treating with anti-HER2 monoclonal antibodies and pyrotinib.