Recently, a series of ESR1 mutations were identified in patients with metastatic ER+ breast cancer, who have progressed on aromatase inhibitors and other endocrine therapies (Jeselsohn et al., 2014; Li et al., 2013; Merenbakh-Lamin et al., 2013; Robinson et al., 2013; Toy et al., 2013). The gene discussed is CYP19A1; the disease is breast cancer.