In particular, early-phase clinical trials reported promising anti-tumor activity of the anti-HER2 antibody-drug conjugates (ADC) Trastuzumab-Deruxtecan and Trastuzumab-Duocarmazine in patients traditionally classified as having HER2-negative breast cancer though exhibiting HER2-low-positive expression (IHC scores 1+ or 2+ in the absence of HER2 gene amplification by ISH)1,2. Here, ERBB2 is linked to breast carcinoma.