Molecular classification of soft tissue sarcomas and its clinical applications

Sarcomas are a heterogeneous group of tumors that are traditionally classified according to the morphology and type of tissue that they resemble, such as rhabdomyosarcoma, which resembles skeletal muscle. However, the cell of origin is unclear in numerous sarcomas. Molecular genetics analyses have not only assisted in understanding the molecular mechanism in sarcoma pathogenesis but also demonstrated new relationships within different types of sarcomas leading to a more proper classification of sarcomas. Molecular classification based on the genetic alteration divides sarcomas into two main categories: (i) sarcomas with specific genetic alterations; which can further be subclassified based on a) reciprocal translocations resulting in oncogenic fusion transcripts (e.g. EWSR1-FLI1 in Ewing sarcoma) and b) specific oncogenic mutations (e.g. KIT and PDGFRA mutations in gastrointestinal stromal tumors) and (ii) sarcomas displaying multiple, complex karyotypic abnormalities with no specific pattern, including leiomyo-sarcoma, and pleomorphic liposarcoma. These specific genetic alterations are an important adjunct to standard morphological and immunohistochemical diagnoses, and in some cases have a prognostic value, e. g., Ewing family tumors, synovial sarcoma, and alveolar rhabdomyosarcoma. In addition, these studies may also serve as markers to detect minimal residual disease and can aid in staging or monitor the efficacy of therapy. Furthermore, sarcoma-specific fusion genes and other emerging molecular events may also represent potential targets for novel therapeutic approaches such as Gleevec for dermatofibrosarcoma protuberans. Therefore, increased understanding of the molecular biology of sarcomas is leading towards development of newer and more effective treatment regimens. The review focuses on recent advances in molecular genetic alterations having an impact on diagnostics, prognostication and clinical management of selected sarcomas.