Two phase III clinical trials, NCT03975647 and NCT04457596, aim to compare the combination of tucatinib and T-DM1 with T-DM1 monotherapy in patients with inoperable locally advanced or metastatic HER2-positive breast cancer and in patients with residual disease post-neoadjuvant and HER2-targeted treatment (O Sullivan et al., 2021). This evidence concerns the gene ERBB2 and breast carcinoma.