In doxorubicin-resistant breast cancer cell line MCF-7/ADR, this was accompanied by increased levels of cholesterol esters, phosphatidylinositol, and sphingomyelin in the membrane [45], resulting in a more rigid membrane, which together with a P-glycoprotein efflux pump prevented doxorubicin import [46]. Here, ABCB1 is linked to breast cancer.