MCL-1 is an anti-apoptotic member of the Bcl-2 family originally isolated from the ML-1 human myeloid leukemia cell line. Similar to BCL2 and BCL2L1, MCL1 can interact with BAX and/or BAK1 to inhibit mitochondria-mediated apoptosis. Mcl-1 is critical for the proliferation and survival of myeloma cells in vitro, and overexpression of Mcl-1 protein in myeloma cells is associated with relapse and short event-free survival in multiple myeloma patients. Recent studies show that MCL-1 is upregulated in numerous haematological and solid tumour malignancies. Therefore, MCL-1 has been suggested as a potential new therapeutic target.