Solitary fibrous tumors are immunophenotypically distinct from mesothelioma(s)

Solitary fibrous tumor is a soft tissue tissue tumor of unknown histogenesis. Based upon histologic similarities and CD-34 expression, it has been suggested that these neoplasms bear some relationship to mesothelioma, and may represent its extra-pleural equivalent.

In order to further investigate this possible relationship, we examined a series of five dermal and five extra-cutaneous solitary fibrous tumors with antibodies directed against the mesothelial markers calretinin and HBME-1.

All the lesions failed to stain with the antibodies tested. This suggests 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(-).

The histogenesis of solitary fibrous tumor remains elusive. It is unlikely that tumor location or tumor de-differentiation accounts for the dichotomous staining properties, as these neoplasms show a similarly benign histologic appearance regardless of location.