HER2-low tumors, although difficult to detect accurately, are proving increasingly to be a variation of breast cancer that while showing no benefit from traditional HER2-based therapies, including Trastuzumab and/or lapatinib (Belizario and Loggulo, 2019), are responsive to antibody-drug conjugates (ADC) including Trastuzumab-deruxtecan (T-Dxd) (Baez-Navarro et al., 2022). The gene discussed is ERBB2; the disease is breast carcinoma.