Disruption of STAT3 signaling pathways leads to the inhibition of Bcl-xl, Mcl-1, and Bcl-2 (Catlett-Falcone et al., 1999; Epling-Burnette et al., 2001; Bhattacharya et al., 2005) and activates the expression of the proapoptotic protein Bax (Nielsen et al., 1999) in cancer cells. This evidence concerns the gene MCL1 and cancer.