The diagnosis of<unk>  is typically made based on histology and is confirmed by the presence of t(X;18) chromosomal translocation. Histopathology Two cell types can be seen microscopically in<unk> . One fibrous type, known as a spindle or sarcomatous cell, is relatively small and uniform, and found in sheets. The other is epithelial in appearance. Classical<unk>  has a biphasic appearance with both types present.<unk>  can also appear to be poorly differentiated or to be monophasic fibrous, consisting only of sheets of spindle cells. Some authorities state that, extremely rarely, there can be a monophasic epithelial form which causes difficulty in differential diagnosis. Depending on the site, there is similarity to biphenotypic sinonasal sarcoma, although the genetic findings are distinctive. Like other soft tissue sarcomas, there is no universal grading system for reporting histopathology results. In Europe, the Trojani or French system is gaining in popularity while the NCI grading system is more common in the United States. The Trojani system scores the sample, depending on tumour differentiation, mitotic index, and tumour necrosis, between 0 and 6 and then converts this into a grade of between 1 and 3, with 1 representing a less aggressive tumour. The NCI system is also a three-grade one, but takes a number of other factors into account. Immunohistochemistry (IHC):<unk> 18-fusion specific antibody and<unk> X-CT antibody are highly sensitive and specific for<unk>  and when used together may obviate the need for molecular testing in most cases. Cytokeratin is typically expressed, at least focally. TLE1, BCL2 and CD99 may be positive but lack specificity. Molecular biology Most, and perhaps all, cases of<unk>  are associated with a reciprocal translocation t(x;18)(p11.2;q11.2). There is some debate about whether the molecular observation itself is definitive of<unk> . The diagnosis of<unk>  is typically made based on histology and is confirmed by the presence of t(X;18). This translocation event between the<unk> 18 gene on chromosome 18 and one of 3<unk> X genes <unk> X1,<unk> X2 and<unk> X4) on chromosome X causes the presence of an<unk> 18-SSX fusion gene. The resulting fusion protein brings together the transcriptional activating domain of<unk> 18 and the transcriptional repressor domains of<unk> X. It also incorporates into the SWI/SNF chromatin remodeling complex, a well known tumor suppressor.<unk> 18-SSX is thought to underlie<unk>  pathogenesis through dysregulation of gene expression. There is some association between the<unk> 18-SSX1 or<unk> 18-SSX2 fusion type and both tumour morphology and five-year survival.
Synovial sarcoma
Biphenotypic sinonasal sarcoma
Osteochondroma
Osteoblastoma
Osteosarcoma
Enchondroma
Ewing's sarcoma
Chondrosarcoma