Medullary thyroid carcinoma in female BALB/c mice. A report of 3 cases with ultrastructural, immunohistochemical, and transplantation data.

Medullary thyroid carcinoma (MTC) is a neoplasm derived from thyroidal C cells. This tumor occurs spontaneously in several animal species and is relatively common in certain strains of rats. Descriptive reports of such neoplasms in mice, however, have not been published. From several studies using female BALB/c mice, 3 animals were identified that had thyroid neoplasms histologically compatible with MTC. All three primary neoplasms and a first generation transplant from one of them contained calcitonin. Somatostatin was identified in two of three primary thyroidal neoplasms and in the first-generation transplant. Ultrastructurally, the neoplastic cells of the first-generation transplant contained membrane-bound dense-core granules that resembled those seen in normal mouse C cells. Intracisternal Type A retrovirus particles were also identified in neoplastic cells in this case. Transplantation of one of the neoplasms yielded subcutaneous masses averaging 2 cm in diameter by 3 months following transplantation in the second-generation recipients. These neoplasms resemble MTCs of man, rat, and other species and may prove of value for comparative morphologic and endocrinologic studies of C cell neoplasms and for studies of factors that regulate the synthesis and secretion not only of calcitonin but also of a variety of regulatory peptides, including somatostatin.