Solitary fibrous tumors are immunophenotypically distinct from mesothelioma(s)

Introduction: Solitary fibrous tumor is a soft tissue tissue tumor of unkno wn histogenesis. Based upon histologic similarities and CD-34 expression, i t has been suggested that these neoplasms bear some relationship to mesothe lioma, and may represent its extra-pleural equivalent. Methods: In order to further investigate this possible relationship, we exa mined a series of five dermal and five extra-cutaneous solitary fibrous tum ors with antibodies directed against the mesothelial markers calretinin and HBME-1. Results: AU the lesions failed to stain with the antibodies tested. This su ggests that despite some similar histologic and immunophenotypic features, these lesions are not immunophenotypically identical. Mesotheliomas are CD- 34-(+), calretinin(+), HBME-1(+), while solitary fibrous tumors are CD-34(), calretinin(-), HBME-1(-). Conclusions: The histogenesis of solitary fibrous tumor remains elusive. It is unlikely that tumor location or tumor de-differentiation accounts for t he dichotomous staining properties, as these neoplasms show a similarly ben ign histologic appearance regardless of location.