Given our recent observation that ABCG2 expression is associated with poor prognosis in patients harboring luminal A subtype breast tumors (TCGA data analysis, unpublished), we utilized the luminal breast adenocarcinoma cell line MCF-7 (very low ABCG2 expression) and its mitoxantrone (MX)-derived, ABCG2-overexpressing subline MCF-7/MX to perform the study. This evidence concerns the gene ABCG2 and breast adenocarcinoma.