ERBB2 and breast cancer: For instance, when tucatinib is used in combination with trastuzumab and capecitabine to treat HER2+ metastatic BC, elevated ALT is observed in 46% of patients who receive tucatinib, compared with 27% of those receiving trastuzumab and capecitabine alone.[17] Consequently, it is recommended to monitor liver function regularly before and during treatment.