Malignant lymphoma in macaques: a clinicopathologic study of 45 cases.

Malignant lymphoma was diagnosed in 42 rhesus macaques (Macaca mulatta) and 3 stumptail macaques (M. arctoides) between February 1969 and December 1977. The distribution of tumor masses in the tissues of individual animals varied widely. Solitary tumor masses were present in 14 animals and multiple masses in the remaining 31 animals. Visceral lymph nodes, gastrointestinal tract, heart, and kidneys were most commonly affected. Peripheral lymph nodes were rarely involved. Most malignant lymphomas were of an undifferentiated cell type, although tumors of histiocytic, lymphocytic, poorly differentiated, and mixed lymphocytic and histiocytic cell types were also observed. Concurrent bacterial and/or viral infections were evident in 30 of the 45 macaques with malignant lymphoma. Amyloidosis was present in 9 animals. This high incidence of malignant lymphoma suggested that their immune responses were abnormal. The development of malignant lymphoma in the macaques may have been secondary to or enhanced by immunodeficiency.