Apport des analyses moléculaires à la classification anatomopathologique des sarcomes

Abstract

Conventional histology and immunohistochemistry remain the basic tools for the diagnosis and classification of sarcomas. However, molecular biology can enrich the pathologists analysis: the identification of a specific molecular abnormality can confirm diagnosis, rule out a differential diagnosis, and sometimes provide prognostic information. About 15% of sarcomas bear a specific translocation, such as rearrangements of SS18 (SYT) [synovial sarcoma], DDIT3 (CHOP) [myxoid liposarcoma], FUS (TLS) [low-grade fibromyxoid sarcoma, myxoid liposarcoma], FOXO1 (FHKR) [alveolar rhabdomyosarcoma], PDGFB (dermatofibrosarcoma protuberans), and ALK (inflammatory myofibroblastic tumor). Rearrangements of the EWSR1 gene are less specific as found in many sarcomas (Ewing sarcoma, desmoplastic round cell tumor, clear cell sarcoma, myxoid liposarcoma, andmyoepithelioma). The search for an amplification of MDM2 gene is a sensitive and specific tool for the diagnosis of atypical lipomatous tumors/welldifferentiated liposarcomas and dedifferentiated liposarcomas (ALT/WDL). The same molecular abnormality can be observed in several tumor types, emphasizing the importance of integrating the results of any molecular study within clinical, morphological, and immunohistochemical context: ASPSCR1 (ASPL)-TFE3 translocation can be observed in alveolar soft tissue sarcoma but also in juvenile renal carcinomas, ETV6 (TEL)-NTRK3 (TRKC) translocation in infantile fibrosarcoma and secretory breast carcinoma, ALK rearrangements in inflammatory myofibroblastic tumors, anaplastic lymphomas, and lung adenocarcinomas. In some cases immunochemistry can highlight the consequence of a molecular abnormality: MDM2 overexpression in ALT/WDL, loss of INI1 expression in rhabdoid tumors and epithelioid sarcoma, and overexpression of ALK in inflammatory myofibroblastic tumors.