The role of molecular pathology in mediastinal sarcomas

Mediastinal sarcomas represent rare neoplasms of mesenchymal origin. Most published data on mediastinal sarcomas is primarily derived from small series and case reports. Although rare, primary mediastinal sarcomas have a clinically aggressive course with worse 10-year survival rates than other types of mediastinal tumors, highlighting the importance of adequate diagnosis of these lesions. The diagnosis of mediastinal sarcomas is complicated by the varied histologic subtypes of tumors that can occur and which can sometimes display overlapping clinical, morphological, imaging, and immunohistochemical features. Cytogenetic analysis and more recently, molecular techniques, have provided new methods by which these tumors can be differentiated. Sarcomas occurring within the mediastinum are an extremely heterogenous group of tumors, although the specific incidence of the different subtypes of mediastinal sarcomas varies among studies, there is a subset of lesions that appear to occur more commonly across most published studies. These tumors include synovial sarcoma, liposarcoma, malignant peripheral nerve sheath tumor (MPNST), small round blue cell sarcomas (including Ewing sarcoma) and leiomyosarcoma (LMS). Other rare sarcoma subtypes may also less commonly occur within the mediastinum. Many of these sarcomas have specific, recurrent genetic abnormalities that can be identified through cytogenetic and molecular testing allowing for accurate diagnosis. This review aims to cover the role of molecular pathology, specifically with regards to diagnosis, as well as discuss the salient molecular genetic features of the various types of sarcoma that occur within the mediastinum. In addition, the various types of cytogenetic and molecular diagnostic tests available for the diagnosis of different types of sarcomas will be reviewed.