Morphologic classification and incidence of hematopoietic neoplasms in the Sprague-Dawley rat.

Hematopoietic and related neoplasms were morphologically studied in a total of 1,765 male and 1,765 female Sprague-Dawley rats from 6 chronic toxicity studies conducted at a large toxicology testing laboratory. The most common types of lymphoid neoplasms seen included the lymphoblastic lymphoma (0.65%) and the large granular lymphocyte lymphoma (LGL, Fischer or mononuclear cell leukemia) (0.60%). The most common type of nonlymphoid neoplasm with morphologic features similar to lymphoid tumors was histiocytic sarcoma (1.1%). A small number of cases of myelogenous leukemia were also seen. Additional work is needed in the classification of hematopoietic neoplasms in rats including refined immunomorphological studies.