Even though AREG has not demonstrated the high sensitivity or specificity required for its use as a biomarker for early prognosis of breast cancer in a population (46), high AREG levels are able to confer resistance to trastuzumab treatment, probably by promoting sustained phosphorylation of the PI3K/AKT and MAPK/ERK pathways, even after the use of this drug (47). Here, AREG is linked to breast cancer.