HER2-low corresponds to the subgroup of HER2-negative breast cancer that expresses some degree of protein in the membrane as characterized by IHC 1+ or 2+/non-amplified according to the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2018 guidelines, updated in 2023 (128, 129). This evidence concerns the gene ERBB2 and breast carcinoma.