Metastatic large intestinal adenocarcinoma in two rhesus macaques (Macaca mulatta).

Spontaneous colonic adenocarcinomas were diagnosed in two rhesus macaques (Macaca mulatta). Although both tumors caused partial obstruction of the colon, they were histologically different. One resembled the commonly described "napkin-ring" adenocarcinoma similar to those found in the descending and sigmoid colon of humans. The other neoplasm, a "tubular" lesion, invaded the full thickness of the colonic wall at the ileocecal-colonic junction. Both tumors were associated with metastasis, which is uncommon in the rhesus monkey.