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Four solid tumours (one haemangiopericytoma, one haemangioendothelioma, one spindle-cell sarcoma and one mammary carcinoma) in dogs were analysed cytogenetically. In the haemangiopericytoma, an additional small chromosomal segment was present. Very complex changes including centric fusions and symmetric meta-centrics 1, 6, 10 and 12 were conspicuous in the highly unbalanced karyotype of the haemangioendothelioma. Complex changes, particularly many centric fusions and a tandem translocation 4/14, were features of the spindle-cell sarcoma. One centric fusion and a symmetric metacentric 13 were present in the mammary carcinoma.

Fourteen guinea pig tumors were received by the Purdue University Animal Disease Diagnostic Laboratories over a period of 5 yr. Among them were 2 mammary gland adenocarcinomas, a mammary gland adenoma, a malignant mixed tumor of the mammary gland, a Schwannoma, 2 limpomas, an inflammatory polyp of the ear canal, a uterine fibroma, 3 trichoepitheliomas, an undifferentiated carcinoma, and a histiocytic lymphosarcoma. The pathologic features of these neoplasms were presented in this report.

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.