Pgp1 (MDR1) expression, frequently detected in both solid and hematologic malignancies, as well as in cancer stem cells, is a marker of chemoresistance and decreased survival in leukemia, lymphoma, osteosarcoma, small-cell lung cancer, ovarian cancer, breast cancer, and other malignancies [2], [3], [4]. Here, ABCB1 is linked to breast cancer.