Spontaneous retroperitoneal liposarcoma in a free -ranging golden-headed lion tamarin (Leontopithecus chrysomelas), Brazil

Marina G. Bueno, Camila V. Molina, Maria C. M. Kierulff, Alcides Pissinatti, José Luiz Catão-Dias, Josué Díaz-Delgado

Primary connective tissue neoplasia is uncommon in nonhuman primates (NHPs). Those of adipocytic origin, especially malignant ones, are rare and there are only few reported liposarcoma cases. Herein, we report a retroperitoneal liposarcoma in a free-ranging golden-headed lion tamarin (GHLT; Leontopithecus chrysomelas). A juvenile, male GHLT was found at the “Serra da Tiririca” State Park, Rio de Janeiro state. The animal was captured on the ground and on physical examination presented apathy, hyporexia, and distended abdomen. The animal was found dead two days after admission. On necropsy examination, upon dissection of the peritoneum the caudoventral abdomen and pelvic cavity were occupied and distended by a 10 cm in diameter, pale tan to yellow, firm, well-demarcated mass that was attached to the pubic ligament focally. Microscopically, the retroperitoneal mass consisted of a well-demarcated, partially encapsulated, moderately cellular, expansive and locally infiltrative neoplasm that was largely composed of adipocytic lobules intermingled with variably large fibromyxoid foci, supported by fibrovascular stroma. In adipocytic areas, tumor cells resembled maturing adipocytes of various sizes, with large cytoplasm occupied by a single clear vacuole that peripheralized oval, hyperchromatic nuclei with inconspicuous nucleoli. In fibromyxoid foci, dedifferentiated spindle tumor cells had mild eosinophilic fibrillar cytoplasm with poorly demarcated borders and oval nuclei with stippled chromatin and few small nucleoli. Anisocytosis and anisokaryosis were mild to moderate for both tumor cell patterns; mitotic figures averaged one per ten high-power fields (400x). Additional tumor cell features included occasional binucleation, multinucleation, focal nuclear atypia and hyperchromasia. Thus, a diagnosis of retroperitoneal atypical lipomatous tumor well-differentiated liposarcoma (ALT/WDL) with myxofibrosarcoma-like dedifferentiation was most plausible. This tumor subtype in a free-living GHLT is novel and atypical; it contributes to expand knowledge on neoplasia in neotropical NHPs. Liposarcomas should be included in the differential diagnosis for abdominal distention and/or intraperitoneal masses in NHPs.

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