Extraskeletal myxoid chondrosarcoma
Extraskeletal myxoid chondrosarcoma (EMC) is a rare low-grade malignant mesenchymal neoplasm of the soft tissues, that differs from other sarcomas by unique histology and characteristic chromosomal translocations. There is an uncertain differentiation (there is no evidence yet showing that EMC exhibits the feature of cartilaginous differentiation) and neuroendocrine differentiation is even possible. Classification. EMC was firstly described in 1953 by Stout et al. when they discussed the different species of extraskeletal chondrosarcoma, but EMC concept was firstly proposed in 1972 by Enzinger et al. Brody thought that this was a unique low-grade malignancy with a  low growth rate and both clinically and histopathologically distinct anamnesis beside the typical chondrosarcomas. However, the parental line of EMC cells remains indeterminate. According to the most recent edition of the World Health Organization Classification of Tumors of Soft Tissue and Bone, EMC has been classified as a type of soft tissue tumor with uncertain differentiation. Recent statistics demonstrate that EMC shows a higher incidence of local recurrence, metastasis and patient mortality and therefore are classified as mean-grade malignancies. EMC is rare and accounts for less than 3% of soft tissue tumors. It mainly affects adults with an average  age of about 54 years (age range 29 to 73 years) and is more common in males, the ratio of male to female is 2:1. Diagnosis. EMCS appears clinically as a slowly developing mass of soft tissue associated with pain and tenderness. Two-thirds of EMC tumors are primarily found in sub-fascia soft tissues of the proximal extremities and limb girdles, especially the thigh and popliteal fossa. The average tumor size is about 9.3 cm (3.3–18 cm). Uncommon locations are the distal extremities, the paraspinal part and the head and neck region.  Incidence of the head and neck  region is less than 5%. Cytogenetics. The cells in EMC tumors do not express specific tumor marker proteins that would help in diagnosing this disease. For example, less than 20% of EMC tumor cases contain cells that express the S100 protein whereas many other tumor types contain cells that express S100 protein in most or all cases (see Pathology of S100 protein). The cytogenetics of this tumor reside in the reciprocal translocations of the 9q22 locus with chromosomes 3q11, 15q21, 17q11, and 22q12. Other cytogenetic events can be observed but are not characteristic. The most common translocation includes the EWSR1  locus at 22q12 and the NR4A3 (also known as TEC and CHN) locus at 9q22. As often can be seen in chimeric transcripts including EWSR1, the transactivation domain of EWSR1 is fused to the DNA-binding domain of NR4A3. Several types of fusion products can be observed, depending on which exons are involved. NR4A3 is an orphan nuclear receptor that is able to activate the FOS promoter and plays a role in the regulation of hematopoietic growth and differentiation. In EMC the DNA-binding domain is constant and the transactivation domains of several genes are involved. These genes include "TAF2N