Expression of CD34 by solitary fibrous tumors of the pleura, mediastinum, and lung.

Solitary fibrous tumors are rare neoplasms that most commonly involve the pleura, mediastinum, and lung. Because they lack distinctive histologic features, immunologic staining has frequently been employed to exclude other neoplasms in the differential diagnosis. Their reported phenotype to date is generally negative, notably for muscle-type actins, desmin, keratin, and S-100 protein. Although this testing is of some help, it does not serve to distinguish all processes in the differential diagnosis, and when it does, it places too great an emphasis on a negative finding to make a diagnosis. We report here that CD34 monoclonal antibodies reacted with 11 of 14 solitary fibrous tumors in paraffin sections. Thus, they provide a positive marker that distinguishes the solitary fibrous tumor from most elements in the differential diagnosis.