BCOR is a ubiquitously expressed nuclear protein that is a transcriptional corepressor important in several cellular processes. Somatic, nonsense and frameshift mutations throughout BCOR have been reported in approximately 7% of chronic myelomonocytic leukemia, 4% of patients with myelodysplastic syndrome(MDS), 4% of primary acute myeloid leukemia and appear to be associated with RUNX1 and DNMT3A mutations . Also, BCOR mutations may be enriched among cases of AML lacking NPM1, CEBPA, FLT3-ITD, IDH1 and MLL-PTD alterations. BCOR mutations tend to be subclonal in MDS, clonal in primary AML and are believed to have significance as loss of function mutations in a tumor suppressor gene that affect the functional allele in male and female patients. The presence of BCOR mutation in patients with MDS and AML has been associated with poorer overall survival according to some studies.