Cytogenetics and molecular biology of soft tissue tumors.

Characteristic genetic aberrations have been identified in many soft tissue tumors, and it is likely that several of these aberrations, e.g., the translocation of chromosomes X and 18 in synovial sarcoma, will play an increasing diagnostic role. It is fascinating that most of the consistent soft tissue tumor translocations result in fusion genes, and these fusion genes encode proteins, which in turn regulate the expression of other genes. Thus, many soft tissue tumor translocations represent the first steps in complicated cascades of events contributing to deregulated tumor cell growth. Although a number of translocations appear to be useful in diagnosis, it should be emphasized that cytogenetic and molecular detection of chromosome translocations and gene fusions is not always straightforward. Cytogenetic and molecular analyses are perhaps best reserved for the subgroup of undifferentiated small round cell or spindle cell sarcomas, which remain unclassified after histological, immunohistochemical, and ultrastructural studies. Tumor specimens frozen at -70 degrees C can be used subsequently for FISH and PCR studies, although the opportunity to karyotype such specimens is lost upon freezing.