The incidence of myelogenous leukemia by repeated skin painting with 20-Methylcholanthrene in RF mice was 29.5% and the mode of development was invertigated, The peripheral blood pictures showed a hypochromic anemia, leukopenia and eosinophilia in the pre-leukemic to intial leukemic stage. In the early leukemic stage, there was a slight leukocytosis with a few myeloblasts. The progressive leukemic stage was characteriged by a hypochromic anemia, anisocytosis, polychromasia, reticulocytosis, thrombocytopenia and leukocytosis with an increase of myeloblasts.
The imprint preparations revealed an increase of neutrophllic cell series in the pre-leukemic stage; and an increare of myeloblasts in the early to progessive leukemic stage, The spleen and lymphnodes showed evidence of neutrophilic cell infiltration in the early to progessive leukemic stage.
Histologically the bone-marrow began to show a slight increase of myeloblasts and other neutrophilic cells in the initial leukemic stage. In the early to progressive leukemic stage, a diffuse proliferation of myeloblasts filled the bone-marrow and invaded the surrounding muscles. There was a slight to moderate leukemic infiltration in the lymphnodes and spleen. The liver showed a leukemic infiltration in the periportal, perivascular spaces and around the central veins.
Bone-marrow tissue cultures showed a hypoplastic pattern in the pre-leukemic stage, a transitional pattern in the initial leukemic stage and a leukemic pattern in the early to progressive leukemic stage, The spleen and lymphnodes assumed a hypoplastic pattern in the initial leukemic stage and a transitional to leukemic pattern in the early to progessive leukemic stage. Of the entire skeletal systems, the lumbar vertebrae, femur and acetabulum fist showed hypoplostic which.was followed by a leukemic transformation.