ERBB4 and breast neoplasm: Most breast tumors with cutaneous metastases are human epidermal growth factor receptor 2 (HER2)-positive subtype; anti-EGFR molecules, such as Trastuzumab and pertuzumab, have exhibited disappointing results, due to the lack of specificity and frequent adverse side effects; however, Pyrotinib (approved only in China), a new small-molecule tyrosine kinase inhibitor that irreversibly blocks EGFR and HER2, as well as human epidermal growth factor receptor 4 (HER4), may have a dual therapeutic impact against HER2 and mucin 1, improving the outcome of patients [23,24].