1989 Volume 2 Issue 1 Pages 73-83
The incidence and histopathological features of spontaneous thyroid, parathyroid, and pancreatic islet tumors encountered in long-term oncogenicity studies using F344 rats or B6C3F1 mice were investigated. Spontaneous C-cell tumors of the thyroid were found at high incidence in both sexes of F344 rats, whereas pancreatic islet-cell tumors were only observed at high incidence in males. All tumors were usually found in old animals, and were rare in young and middle aged rats. In general, the incidences of endocrine tumors in B6C3F1 mice were very much lower, although follicular cell tumors of the thyroid were sometimes observed. In the endocrine system, the follicular cell of the thyroid is the most susceptible to chemical carcinogens. Carcinogen-induced tumors can be distinguished from spontaneous lesions due to their higher incidence, earlier induction, multiplicity, and increased evidence of invasion and metastasis.
