Medullary thyroid carcinoma in the Syrian golden hamster: an immunohistochemical study.

Spontaneously occurring thyroid neoplasms exhibiting solid and/or anaplastic growth patterns in the Syrian golden hamster have been thought to be derived from follicular cells. Eight neoplasms of this type have been analyzed immunohistochemically and have been classified as medullary thyroid carcinomas (MTC) on the basis of their content of calcitonin (CT). Well differentiated MTCs in this species were composed of polyhedral cells showing uniform CT immunoreactivity while the poorly differentiated MTCs most often had spindle patterns of growth with marked variation in CT immunoreactivity.