T-DXd was initially approved for patients with HER2-positive breast cancer who had received at least two prior lines of treatment based on DESTINY-Breast 01 [13], this drug was then approved in the second line setting based on DESTINY-Breast 03 [29] and there are ongoing studies to assess the efficacy of this agent in the first line setting (DESTINY-Breast 09, NCT04784715). The gene discussed is ERBB2; the disease is breast cancer.