Early metastatic stage of 2,7‐FAA‐induced leukemia in rats

The development from primary focus to metastasis was histologically investigated in 2,7-FAA-induced leukemia in rats. The Wistar and Sprague-Dawley strains were used, and the results were similar in both strains. The spread of lesions was classified as solitary, scattered or diffuse. Scattered leukemia lesions were divided into two groups: A and B: (A) consisted of one or a few conspicuously large foci and many small foci, and (B) had no such large foci. The interval from the first appearance of orthochromatic erythroblasts to autopsy was short in animals with solitary lesions, slightly longer in those with scattered lesions in group (A), and still longer in group (B). Conspicuously large foci were predominantly localized in the bone marrow, while small foci were scattered in the bone marrow, spleen and liver. The (A) scattered lesions were considered to represent the early metastatic stage, since they consisted of the combination of large and small foci, and the time interval from the first appearance of erythroblasts to autopsy was between that of solitary lesions and (B) scattered lesions. The leukemia induced in rats by 2,7-FAA occurred predominantly in the bone marrow, which was the primary site. It was thought that this leukemia spread rapidly to other regions of the bone marrow, and to the spleen and liver, by hematogenous metastasis.