Morphological classification and incidence of thyroid tumors in untreated aged mice.

The authors reviewed a total of 83 thyroid neoplasms in several strains of untreated mice. The 83 thyroid neoplasms consisted of 76 adenomas and 7 carcinomas. The adenomas and carcinomas were divided into the following three morphological types: papillary, follicular, and solid. The papillary adenoma was the most common type. The tumors were more common in female than male mice. The incidence ranged from 0.13% in BALB/c females to 8.6% in C3H-MTV females.