Soft tissue tumors are a very heterogeneous group of tumors in terms of histogenesis, morphology, cytogenetics, molecular biology, clinical manifestation, and prognosis. Their spectrum is fascinating for morphologists and basic scientists alike. Yet precisely this variability in the morphologic manifestation of soft tissue tumors, specifically their histologic and cytologic patterns, presents great difficulties to any effort to categorize them. Although many soft tissue tumors are today defined not only by histology but also by immunohistochemical, cytogenetic, and molecular biological findings, the histogenesis of many soft tissue tumors, in particular malignant ones, continues to be unknown. This is associated with the fact that the actual precursor cells