[Morphology and molecular biology of malignant soft tissue sarcomas]

Malignant soft tissue tumors are classified and named according to cellular differentiation and thus the non-neoplastic soft tissue they imitate. The topical WHO classification already comprises more than 140 entities and tumor subtypes, but the process of defining new tumor variants will go on. Questions of nomenclature are discussed briefly with laying special emphasis on the non-undisputed concept of malignant fibrous histiocytomas. Without doubt, this diagnosis is made too frequently by which it has become to a collective name for unclassifiable pleomorphic sarcomas. For the time being nobody is able to say whether or not the malignant fibrous histiocytoma will remain an entity. Likely, fibrosarcomas and hemangiopericytomas are defined as exclusion diagnosis, as well. The diagnosis of malignant soft tissue tumors is based on recognizing the cellular line of differentiation. This is frequently possible at light microscopic level, sometimes additional diagnostic methods are required. The most important adjunct method is immunohistochemistry. Because aberrant differentiations and unexpected immunohistochemical reactions are known the use of a panel of antibodies is necessary. In the last years soft tissue tumors has increasingly been characterized by molecular biological methods. The results are of significance for understanding sarcoma pathogenesis and may be used for diagnosis, as well. Chromosome translocations are explained and rhabdomyosarcomas are taken as example for demonstrating the diagnostic significance of molecular biological/cytogenetic findings. Molecular biology may also aid in defining the histopathologic features of an entity as shown for intraabdominal desmoplastic small cell tumors. Eventually, heterogeneity in soft tissue sarcomas is addressed and discussed in view of its importance for diagnosis, classification and therapy as well as for development of sarcoma progression.