The pathology of murine myelogenous leukemias.

Murine myelogenous leukemias can be classified into several distinct subgroups based on morphology, cytochemical staining, and immunoreactivity. The leukemias invariably involve the spleen and the extent of infiltration into other tissues is variable. The myelogenous nature of the leukemia is readily apparent in well-differentiated leukemias on the basis of morphology; with poorly differentiated leukemias, positive staining with chloroacetate esterase, nonspecific esterase, and certain monoclonal antibodies such as Mac-1, is helpful to establish myelogenous differentiation. Subgrouping of myelogenous leukemias depends on the presence or absence of monocytic differentiation, as ascertained by staining with Mac-2, electron microscopy or phagocytosis. Leukemias showing no monocytic differentiation can be classified as myeloblastic, corresponding to the FAB M1 and M2 subtypes in humans. Leukemias exhibiting both monocytic and granulocytic features are myelomonocytic, corresponding to the FAB M4 subtype. Tumors with only monocyte differentiation arise primarily as solid tumors in mice, and a leukemic phase is variable.