%0 Case Reports %T Retroperitoneal extraosseous peripheral primitive neuroectodermal tumor in a Formosan serow: case report and literature review. %A Hsieh YH %A Hsu YH %A Lien CY %A Liu CH %A Li WT %J J Vet Diagn Invest %V 31 %N 6 %D Nov 2019 %M 31585511 %F 1.569 %R 10.1177/1040638719879198 %X A 10-y-old female captive Formosan serow (Capricornis swinhoei) was inactive and was azotemic. An autopsy was performed following her death, and multiple irregularly shaped, white-to-gray masses of 0.5-2 cm diameter were noted on both ureters, the left adrenal gland, urinary bladder, and uterus. Microscopically, organs were effaced by a poorly demarcated, highly infiltrative neoplasm, composed of neoplastic round cells arranged in islands, sheets, or nests with occasional rosette formation. The neoplastic cells were small: ≤2 red blood cell (≤ 15 μm) diameter. The neoplastic cells were positive for CD56, CK, FLI-1, and NSE, but negative for desmin, GFAP, melan A, NF, PAX-8, S100, synaptophysin, and vimentin. Therefore, the diagnosis of retroperitoneal extraosseous peripheral primitive neuroectodermal tumor (pPNET) was made. pPNET with FLI-1 expression has not been reported previously in animals, to our knowledge.