According to this classification, cancer cells that express human epidermal growth factor 2 (ERBB, formerly HER2) and not estrogen receptors (ER) are identified as the HER2+ molecular subtype, which represents 15%–30% of breast cancer patients, is an aggressive phenotype, and a predictor of poor outcome (Ban et al., 2020). This evidence concerns the gene ESR1 and breast carcinoma.