Mammary adenocarcinoma in a male squirrel monkey (Saimiri sciureus)

A nodule was identified within the right mammary gland of a 16-year-old mal e squirrel monkey (Saimiri sciureus). The mass was excised and diagnosed as a mammary adenocarcinoma. The monkey developed congestive heart failure 1. 5 years later and was euthanatized. At necropsy, a subcutaneous mass was fo und in the light axillary region. Histologically, the mass was identified a s a lymph node whose architecture was effaced by neoplastic cells resemblin g those of the mammary tumor. Metastasis to internal organs was not observe d. This is the first reported case of a mammary tumor in a New World primat e and the only known case of mammary cancer in a male nonhuman primate.