Deciphering Atypical Signals Present in Fluorescent In Situ Hybridization Assays in the Diagnosis of Soft Tissue Sarcomas.

Soft tissue sarcomas (STS) represent a heterogeneous group of rare tumors of mesenchymal origin. This group of solid tumors includes more than 120 different histotypes commonly difficult to be accurately diagnosed. Thus, differential diagnosis of these tumors is of utmost importance for patients' clinical management and usually includes more than one type of test. Fluorescence in situ hybridization (FISH) is one of the most widely applied methods for the detection of fusion genes that characterize the majority of STS. Our routine diagnostic practice includes FISH assay along with other appropriate molecular tests. Atypical signals have been observed in several cases of FISH assays on STS samples that do not fulfill the established diagnostic criteria for rearrangements. Thus, the aim of this study was to investigate this observation and pinpoint their utility in STS diagnosis.