[Clinicopathological analysis of infantile/congenital fibrosarcomas with rare histological features].

To analyze the clinicopathological features, immunohistochemical (IHC) phentotype,diagnosis and differential diagnosis of infantile/congenital fibrosarcoma (IFS/CFS) with unusual histological features. Five IFS/CFS at Children's Hospital of Fudan University from March 2014 to July 2018 were analyzed for their diagnosis and differential diagnosis. Two cases were males, three cases were females. The clinical manifestation of IFS/CFS was a rapidly-growing and painless mass. There were no specific radiologic features. Histologically, the tumor cells are arranged in intersecting or sheet-like patterns. There were focal hemangioma-like areas in four cases. There were also focal areas of primitive asteroid, short-spindled, and oval tumor cells in three cases. IHC study showed the tumor cells diffusely expressed TLE1(2/5), Vimentin(5/5), and WT1(3/5), in a cytoplastic pattern; they focally expressed CD34(3/5), CD31(3/5), and α-SMA(2/5). Fluorescence in situ hybridization (FISH) detected break-apart positivity of ETV6 gene. Hemangioma-like pattern, myxoid area, and TLE1 expression is very rare in IFS/CFS. Detection of ETV6 gene break-apart by FISH is very helpful in the diagnosis and differential diagnosis of IFS/CFS.