Gene dosage effects of ecotropic viral integration site‐1 (EVI‐1) in hematopoietic stem cells (HSC) and hematological malignancies. EVI‐1 regulates proliferation and maintenance of HSC in a dose‐dependent manner. Activation of EVI‐1 in hematopoietic cells leads to clonal expansion or dysplastic hematopoiesis, whereas onset of full‐blown leukemia requires cooperative genetic events. Hox, Homeobox; Meis, Myeloid ecotropic viral integration site; MLL, Mixed‐Lineage leukemia; Runx, Runt‐related transcription factor.