Here, T-DXd achieved an mPFS of 9.9 vs. 5.1 months (HR 0.50; p < 0.001) and improved OS to 23.4 vs. 16.8 months (HR 0.64; p = 0.001) [19], establishing HER2-low breast cancer as a therapeutically relevant subgroup and redefining the reach of HER2-targeted therapy. This evidence concerns the gene ERBB2 and breast carcinoma.