Recently, a new anti-HER2 ADC, trastuzumab-deruxtecan (Enhertu; AstraZeneca) showed antitumor activity not only in patients with HER2-positive cancer (HER2 3+ and HER2 2+/FISH+) but also in low-HER2–expressing tumors (HER2 1+ and HER2 2+) that were previously categorized as HER2 negative and not eligible for anti-HER2 monoclonal antibody treatment7. This evidence concerns the gene ERBB2 and cancer.