Here, we analysed the molecular mechanism of leukaemogenesis by CALM-AF10.     ///    Leukaemic transformation by CALM-AF10 involves upregulation of Hoxa5 by hDOT1L..     ///    We demonstrate that CALM-AF10 fusion is both necessary and sufficient for leukaemic transformation.     ///    "Thus, our study establishes CALM-AF10 fusion as a cause of leukaemia and reveals that mistargeting of hDOT1L and upregulation of Hoxa5 through H3K79 methylation is the underlying mechanism behind leukaemia caused by CALM-AF10 fusion.. "