Here, we found Bmi1 overexpression in 5-Fu (5-fluorouracil)-resistant MCF-7 cells (MCF-7/5-Fu) derived from MCF-7 breast cancer cells, MDA-MB-231 and MDA-MB-453 breast cancer cells compared to MCF-7 cells, was related with 5-Fu resistance and enrichment of CD44+/CD24- stem cell subpopulation. The gene discussed is BMI1; the disease is breast carcinoma.