Ghanashyam Biswas et al. have proven that TDM–1 is more effective than trastuzumab in preventing relapses in the long term, prolongs progression-free survival (PFS) and improves survival rates in patients with HER2(+) breast cancer, while preclinical studies are promising, in which T–Dxd shows activity against tumors resistant to T–DM1 [68,69,70,71]. The gene discussed is ERBB2; the disease is breast carcinoma.