MCL1 and breast cancer: Myeloid cell leukemia 1 (MCL1), an antiapoptotic BCL-2 family member, is overexpressed in many types of human tumors, including leukemia (20), breast cancer (21), prostate cancer (22), and ovarian cancer (23); and its expression correlates with disease grade and survival-predicting response to anticancer therapies (24, 25).