Pheochromocytoma in Old World Primates (Macaca mulatta and Chlorocebus aethiops).

Pheochromocytoma, a rarely reported adrenal gland neoplasm in Old World primates, was diagnosed in 5 rhesus macaques (Macaca mulatta) and 2 African green monkeys (Chlorocebus aethiops) from 3 research institutions. Age and sex were available for 6 primates. Two males and 4 females were affected, ranging in age from 9 to 31 years. All neoplasms were unilateral and, in the cases reporting the affected gland, 4 involved the right adrenal gland and 2 involved the left. Diagnosis was established by characteristic histologic features. Immunohistochemically, neoplastic cells in all cases expressed chromogranin A and met-enkephalin and were negative for melan-A and inhibin. Six of 7 tumors were positive for β-endorphin. Pulmonary metastases were present in 2 rhesus macaques and portal vein invasion in 1 African green monkey. To the authors' knowledge, this is the first report of malignant pheochromocytoma in Old World primates.