Additionally, we used qRT-PCR assays to assess the mRNA levels of the AR/ESR1 and AR/PGR ratios in four cell lines representative of different BC subtypes (MCF7, BT474, MDA-MB453, and MDA-MB231), as well as in breast tissue from a small group of patients (11 cases) stratified by estrogen receptor (ER) status. The gene discussed is ESR1; the disease is breast cancer.