Morphology of spontaneous Harderian gland tumors in aged B6C3F1 mice.

Spontaneous Harderian gland tumors in B6C3F1 mice were found in 18 (3.1%) (one male had bilateral tumors) of 589 males and 18 (3.0%) of 609 females. The tumor-bearing mice ranged in age from 73 to 109 weeks. These tumors comprised 32 adenomas (86.5%), four adenocarcinomas (10.8%) and one pleomorphic tumor (2.7%); the adenomas were classified, based on the growth patterns, into 17 papillary, nine cystic papillary, five acinar and one cystic types. Two adenocarcinomas grew papillary and invaded surrounding tissues, and the other two grew acinously. The pleomorphic tumor consisted of pleomorphic cells some of which had a keratin-positive epithelial feature and acini lined by atypical epithelial cells.