D2-40-positive solitary fibrous tumors of the pleura: diagnostic pitfall of biopsy specimen.

Solitary fibrous tumor of the pleura (SFTP) is an uncommon spindle-cell neoplasm and is sometimes confused with other spindle-cell tumors, such as sarcomatoid mesotheliomas. D2-40 is a new monoclonal antibody recognizing podoplanin and several studies have confirmed the reliability of D2-40 in the diagnosis of pleural mesothelioma. The authors encountered a case of SFTP that was immunoreactive to D2-40. A 56-year-old woman was admitted to hospital because of an abnormal shadow on a chest X-ray. Percutaneous needle biopsy indicated a spindle-cell tumor showing positive immunoreactivity for CD34, supporting the diagnosis of SFTP. However, the tumor was also immunoreactive to D2-40 and thus malignant mesothelioma could not be ruled out. The tumor was surgically resected to make a definitive pathological diagnosis. The tumor had a patternless architecture and immunohistochemistry was positive for CD34 and D2-40 but was negative for calretinin and cytokeratin 5/6. Therefore a pathological diagnosis of SFTP was made. An additional six tumors diagnosed as SFTP were also tested. Focal immunoreactivity to D2-40 was positive in three out of seven cases, including the first case. Care is required in diagnosing biopsy specimens of D2-40-positive pleural spindle-cell tumors, especially in making the differential diagnosis between SFTP and malignant mesothelioma.