Diagnosis of a Primary Pleomorphic Liposarcoma in a Tree Shrew（Tupaia belangeri subsp. yaoshanensis）

A large spontaneous mass on the dorsal abdomen near the hip joint was found in an aged female Tupaia belangeri subsp. yaoshanensis after 5 years of routine feeding. The tumor in the diseased tree shrew was huge, with an intact surface and no ulceration; however, it caused inconvenience in movement while maintaining a good mental state. After inhalation anesthesia with isoflurane (2%-4%), the tree shrew was euthanized after the tree shrew entered deep anesthesia. Anatomical dissection of the tumor, the tumor boundary was unclear and infiltrated into surrounding tissues. HE staining showed that small focal pleomorphism and large areas of adipocytes were seen in the tumor tissue. The pleomorphic sarcoma area was mainly composed of atypical epithelioid cells with easily visible nuclear divisions. The size of the adipocytes was significantly different, and more pleomorphic adipocytes were seen. The cell volume was large, the nucleus was deeply stained and deformed, the edge was impressed, and the cytoplasm was seen with multiple vesicular lipid droplets. Immunohistochemical results showed that the tumor cells were positive for Vimentin, the small focal polymorphic adipocyte nucleus was positive for S-100, and Ki-67 exhibited a higher proportion of positivity. Combined with HE staining and immunohistochemical results, the spontaneous tumor in this tree shrew was comprehensively diagnosed as pleomorphic liposarcoma.