Ovarian epithelioid trophoblastic tumor in a cynomolgus monkey

Epithelioid trophoblastic tumor (ETT) is an unusual type of trophoblastic tumor, with features resembling carcinoma. In this study, we describe a 4-year-old cynomolgus monkey (Macaca fascicularis) showing, at necropsy, a lobulated mass replacing the left ovary and several nodular lesions within the lungs. Histologically, the mass in the ovary and lung metastases were characterized by nests of epithelioid cells, with intermingled, occasional, multinucleate tumor cells consistent with syncytiotrophoblasts and moderate amount of eosinophilic, hyaline-like material. Immunohistochemically, the tumor cells were diffusely positive for cytokeratins (AE1/AE3) and inhibin-alpha, but only focal immunoreactivity was observed for human chorionic gonadotropin, whereas placental alkaline phosphatase was always negative. On the basis of morphology and immunohistochemical reactivity, tumor cells were identified as intermediate trophoblast.