A unified hypothesis for the histogenesis of the soft tissue sarcomas of unknown origin

At the present time there is still a group of soft tissue sarcomas with an unknown origin. These occur most frequently in the extremities and include the following sarcomas: clear cell, alveolar, synovial, epithelioid, chordoid and small round cell. Most of the studies directed to find their histogenesis are based on finding similarities between normal embryonic or mature tissues of the tenosynovial region and these tumors at the ultrastructural and immunohistochemical level searching for specific markers. In this sense, the results are confusing and the common or different cells responsible for these sarcomas have not yet been isolated. In the present hypothesis it is proposed that the common progenitor of these malignancies is an ectomesenchymal derived tissue related to the tendons, aponeuroses, synovia and menisci called chondroid tissue or pseudocartilage; the evolutionary reasons that support this hypothesis are also discussed here. This also emphasizes the possibility that these sarcomas originate in phylogenetic mature remains and not in the reactivation of embryological cellular groups (Cohnheim's theory).