KPM+ mice coexpressing oncogenic K-ras and PML-RARα develop a lethal APL-like disease. Representative peripheral blood (1000× original magnification), bone marrow (1000× original magnification), spleen (400× original magnification), and liver (400× original magnification) histopathology from age-matched KPM+, KM+, nondiseased KP+, and K+ mice. Insets show representative myeloperoxidase immunohistochemistry of KPM+ and K+ spleen (400× original magnification). Note the predominance of immature mononuclear cells within the marrow and spleen of KPM+ mice compared to KM+, nondiseased KP+, and K+ mice.