Runx1^−/− mice show early onset and high frequency of leukemia with myeloid features in RIM. (A) Kaplan-Meier survival curves of Runx1^+/+ (blue line; n = 17) and Runx1^−/− (red line; n = 16) mice injected with MoMuLV retrovirus. Kaplan-Meier method showed significant difference between the 2 genotypes (P < .001, Mantel-Cox test). Open circles represent censored cases. (B) Necropsy of diseased mice; leukemic mice usually show enlarged spleen (bottom arrow) and liver (top arrow) while T-cell lymphoma mice show enlarged thymus (arrow). (C) Graphs showing frequency of different types of leukemia/lymphoma, groups 1 to 4, in early-onset (≤ 24 weeks) cancers of Runx1^+/+ (n = 19) and Runx1^−/− (n = 34) mice; and frequency of leukemia or lymphoma cases in late-onset cancers of Runx1^+/+ (n = 33) and Runx1^−/− (n = 20) mice. In total, n = 52 for Runx1^+/+ mice and n = 54 for Runx1^−/− mice. (D) Morphology of cells from PB of representative leukemic case from group 1 showing granulocyte (arrow) and monoblast (arrowhead); group 2 showing immature blasts; and group 3 showing T cells and ghost cells (arrows) which are frequently seen in T-cell malignancy.