When breast cancer occurs in AYAs, it differs from that occurring in older women in several ways: a worse prognosis and more-aggressive phenotype, higher proportions of high-grade and later stage tumors, lower estrogen receptor (ER) positivity, and overexpression of human epidermal growth factor receptor 2 (HER2) [1,3,4]. The gene discussed is ESR1; the disease is breast carcinoma.