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

Objective: To analyze the clinicopathological features, immunohistochemical (IHC) phentotype,diagnosis and differential diagnosis of infantile/congenital fibrosarcoma (IFS/CFS) with unusual histological features. Methods: Five IFS/CFS at Children's Hospital of Fudan University from March 2014 to July 2018 were analyzed for their diagnosis and differential diagnosis. Results: 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. Conclusions: 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.