Uterine Epithelioid Trophoblastic Tumour in a Red-tailed Guenon (Cercopithecus ascanius)

Epithelioid trophoblastic tumour (ETT), a rare neoplasm of chorionic-type intermediate trophoblastic cells in the human female, was diagnosed in the uterus of a red-tailed guenon, a non-human primate. The animal, having had two live births, had a recent history of heavy vaginal bleeding. Four years after the last known pregnancy, the animal developed a large invasive mass involving the uterus, right ovary and abdominal wall. The tumour was removed surgically, but at necropsy 1.5 years later was found to have a recurrent neoplasm. Histologically, the original mass consisted of nests and cords of mononuclear intermediate trophoblastic cells whose borders were accentuated by intimately associated eosinophilic hyaline extracellular proteinaceous material. Extensive coalescing areas of necrosis with mineralization surrounding islands of viable neoplastic cells created a “geographical” pattern of necrosis. Immunohistochemical examination revealed that neoplastic cells were diffusely strongly positive for cytokeratin 18, and focally positive for human placental lactogen. The histopathological and immunolabelling patterns were consistent with ETT in human beings. This is the first reported case of epithelioid trophoblastic tumour in a non-human species.