While CYP19A1 amplification is very rare in primary untreated ER+ breast cancers, Magnani et al. [51] found that 21.5% of AI-refractory relapsed tumors to harbor CYP19A1 amplification, suggesting that CYP19A1 amplification is an acquired endocrine therapy resistance mechanism[51]. The gene discussed is CYP19A1; the disease is breast carcinoma.