Indirect fluorescence microscopy revealed that FASN protein was localized primarily in the cytosol of untreated MCF-7 cells, a well-known model of ER+ endocrine therapy-responsive breast cancer, belonging to the luminal A molecular subtype of breast cancer (i.e., ER-positive, HER2-negative, and low proliferative capacity). The gene discussed is FASN; the disease is breast carcinoma.