Mammary neoplasia in the guinea pig (Cavia porcellus).

Mammary tumors are reported in four guinea pigs and the literature is reviewed. It is concluded that mammary adenocarcinomas are second only to pulmonary adenomas as the most common epithelial tumors in the guinea pig. The sex incidence of mammary tumors is almost equal and both young and old animals are susceptible. Mammary tumors are generally locally invasive, rarely metastasize, are often quite large, and very vascular. Surgical excision of mammary tumors is possible but recurrence should be expected if the primary tumor is incompletely removed.