Spontaneously occurring lymphohematopoietic tumors in three young Sprague Dawley rats

To assess the toxicological and pharmacological effects of chemicals, it is important to know what kinds of neoplasms naturally occur in the early life of laboratory animals. In the present study, we identified three spontaneous hematopoietic tumors in three of 52 young female Sprague-Dawley rats used in a pharmacological study. These cases included two rats (Case 1 and 2) from a sesame oil-treated group and one rat (Case 3) from a chemical-treated group in the same single gavage study. Case 1 rapidly lost body weight at 13 weeks of age without any clinical signs and died. Round lymphoid tumor cells were found in the spleen, liver, bone marrow, and pancreas. The tumor cells were immunohistochemically positive for CD3 and PCNA, which is suggestive of malignant T-cell lymphoma. Cases 2 and 3 had rapid body weight loss at 14 and 16 weeks of age, respectively, exhibited severe anemia, hypolocomotion, and decreased body temperature, and were euthanized due to a poor prognosis based on severe clinical signs. Pleomorphic large tumor cells were found in the spleen, liver, bone marrow, lymph nodes, heart, kidneys, lung, pancreas, adrenal glands, pituitary gland, ovaries, Harderian gland, and/or eyes. The tumor cells were immunoreactive for CD34, lysozyme, and PCNA, which is suggestive of myeloid leukemia. These cases might provide useful historical control information for rat toxicity studies.