Our novel functional data using Bcor depletion/deletion unequivocally demonstrate that mutation of Bcor, seen at a higher frequency in in Eμ-Myc lymphomas than lesions in the known cancer genes Trp53, Cdkn2a and Ras, is a ‘driver' oncogenic event and provides mechanistic context to observations by others that mutations in BCOR occur in a range of human malignancies. This evidence concerns the gene BCOR and cancer.