It has been reported that ABCG2is a stem cell marker with high expression in breast cancer and maybe associated with metabolic and signaling pathways such as drug resistance,self-renewal, and invasiveness, and therefore may provide poor prognosis., ABCG2­(+) cell subpopulations in tumors have stem cell-like properties;the central role of ABCG2 in tumor regeneration after chemotherapyhas been suggested. The gene discussed is ABCG2; the disease is breast carcinoma.