MCL1 and breast neoplasm: To extend these in vitro studies, we assessed the copresence of KLF4/5 expression with MCL1, BCL-XL and/or BCL2 in human tumors (Table 1).48, 49 Using a ±1.5 z-score range to define high and low expression groups, we evaluated the mutual exclusivity/inclusivity in 958 human breast tumors that were analyzed by microarray.