Encouraged by the promising phase II study of pyrotinib in combination with capecitabine in HER2-positive metastatic breast cancer [22], we next determined the efficacy of the combination of inetetamab with pyrotinib plus capecitabine, a chemotherapeutic agent acting as a thymidylate synthase inhibitor, in treating HCC1954 tumors, another trastuzumab-resistant breast cancer model [23]. This evidence concerns the gene TYMS and breast cancer.