[Soft tissue sarcomas: clinical application of molecular biology]

Soft tissue sarcomas are rare and heterogeneous tumours. Histological diagnosis is often difficult because of the numerous types and subtypes reported and morphological similarities with benign lesions in certain cases. Molecular analyses performed in an appropriate clinical and histological context improve the patients' management in the case of sarcomas with simple genomic profile: the identification of a specific and objective molecular abnormality can confirm a diagnosis, rule out another one, provide prognostic information, and guide the selection of targeted therapy About 15% of sarcomas bear a specific translocation that can be identified by FISH or RT-PCR. The search for a MDM2 amplification, reflecting the presence of an amplicon in the 12q region, is a sensitive and specific tool for the diagnosis of atypical lipomatous tumors/well-differentiated liposarcomas and dedifferentiated iposarcomas. The presence and the type of KITor PDGFRA activating mutation guide the diagnosis and treatment of GIST. Certain molecular abnormalities are found in several tumour types, emphasizing the importance of integrating the results of any molecular study within the morphological and immunohistochemical context: In France, sarcoma diagnosis is structured around a reference network (RRePS) that provides every pathologist an access to these molecular analysis tools.