If this scenario indeed materializes, all these complexities are likely to become futile exercises, and T-DXd to become an effective treatment option for at least two distinct groups: those with HER2 pathway activation/addiction (HER2 overexpressed or amplified) and those with HER2 protein present (HER2 not overexpressed or amplified), as most or all breast tumors contain some level of HER2 protein. This evidence concerns the gene ERBB2 and breast neoplasm.