T-DXd significantly improved PFS (9.9 vs. 5.1 months, HR 0.50, 95% CI: 0.40–0.63, p < 0.001) and OS (23.4 vs. 16.8 months, hazard ratio 0.64, 95% CI 0.49–0.84, p = 0.001) in patients with HER2-low BC, regardless of the HR status [108]. This evidence concerns the gene ERBB2 and breast cancer.