Adult T cell leukemia. Histological classification and characteristics.

Adult T cell leukemia was classified into two distinct types, monomorphic and pleomorphic, according to their histological and cytological features. The former type is composed of uniform neoplastic cells with round or slightly indented nuclei without any marked deformation. The latter type, on the other hand, occupies a unique position in lymphocytic leukemias with the following characteristics: a) onset in adulthood, b) an acute and subacute course, c) well-differentiated T cell origin of the neoplastic cells, d) pleomorphism of the neoplastic cells with markedly deformed nuclei, e) diffuse proliferation of the neoplastic cells without nodular pattern, f) histologically heterogeneous features of lymph nodes frequently admixing a cluster of normal lymphocytes, proliferation of macrophages and dendritic cells, and well-developed high endothelium venules, g) high incidence of skin lesions due to the infiltration of neoplastic cells, and h) exclusively limited localization of patients' birth places.