Spontaneous Myeloblastic Leukemia in a Young SD Rat

A hematopoietic neoplasm was found in a 14-week-old male Sprague-Dawley (SD) rat. Blood smear examination revealed the existence of numerous blastic cells with large, round or oval nuclei, and scant pale cytoplasm containing no granules. At autopsy, the liver and spleen were markedly enlarged and the right femur showed swelling and hemorrahge. Histopathologically, neoplastic cells infiltrated diffusely in the bone marrow, liver, and spleen, and destroyed their normal architectures. In the bone marrow neoplastic cells invaded into the surrounding tissues, while in the spleen they proliferated from the red pulp. Immunohistochemically, neoplastic cells were positive for lysozyme, while they were negative for hemoglobin, ED-1, OX-7, OX-8, and OX-12. Based on these findings, the present neoplasm was diagnosed as myeloblastic leukemia.