A significant overexpression in estrogen-responsive genes, such as GREB1 and AREG, was observed in estrogen-receptor positive (ER+) breast cancer patients aged 45 years or younger, who had a significantly lower expression of ESR1 compared to older women (age ≥70 years) (Yau et al., 2007). The gene discussed is EREG; the disease is breast carcinoma.