Spontaneous malignant lymphoma in non human primates: a morphologic study of 43 cases

Malignant lymphoma was detected in 42 rhesus monkeys (Macaca mulatta) and one stumptail monkey (M. speciosa) at the California Primate Rsearch Center during the period from February 1969 to June 1974. Previous reports have described some of the epidemiologic, virologic, and transmission studies of this outbreak. This report describes the pathologic lesions observed in these 43 animals. There was widespread variation in the number of organs involved in individual animals was well as the incidence of organ involvement in different animals. Solitary masses were present in 13 animals and multiple masses in the remaining 30. Visceral lymph nodes were involved with the highest frequency, followed by the gastrointestinal tract, heart, kidneys, and adrenal glands, respectively. There was a low incidence of peripheral lymph node involvement, with the exception of 8 monkeys that had retroorbital tumor masses. The neoplasms were classified by using the criteria described by Rappaport. The majority were lymphomas of the undifferentiated cell type, but several were classified as histiocytic or mixed cell types. Eleven of the 43 monkeys had concurrent Mycobacterium avium infections. Eight had herpesvirus infections and 4 had lesions compatible with progressive multifocal leukoencephalopathy. This high incidence of viral and bacterial infections in the animals with malignant lymphoma suggests that their immune systems were compromised.