The HER2CLIMB trial confirmed that tucatinib, in combination with trastuzumab and capecitabine, significantly improves PFS (7.6 months versus 4.9 months for the placebo group) and OS (24.7 months versus 19.2 months for the placebo group) in patients with HER2-positive metastatic BC, including those with brain metastases who often have limited treatment options [82]. This evidence concerns the gene ERBB2 and breast cancer.