The differentiation of sarcomatoid mesothelioma from other cell tumors by light microscopy is quite difficult. The role of immunohistochemistry is also not well defined in its diagnosis. Since sarcomatoid mesothelioma is not always cytokeratin-negative, the distinction between it and sarcoma is not always possible. In this context, the doctors undertook a study to investigate the utility of diagnostic immunohistochemistry for distinguishing sarcomatoid mesothelioma from its histological mimics, high-grade sarcoma and pulmonary sarcomatoid carcinoma.
For its study, the researchers stained the mesotheliomas with sarcomatoid components. They assessed the intensity and distribution of staining with the help of a semi quantitative scale. Only tumors with unequivocal staining were considered positive for tabulation. Then they compared the immunophenotypic profiles of these tumors with 24 high-grade sarcomas. The sarcomatoid carcinomas were also stained for thyroid transcription factor-1 (TTF-1).
The study showed that Cytokeratin 5/6 stained most of the epithelioids but the sarcomatoids were rarely stained. On the other hand, Calretinin and thrombomodulin each stained 70% of sarcomatoid. All 10 sarcomatoids were negative for TTF-1. This led to the conclusion that a wide immunophenotypic overlap exists among different sarcomatoids. Cytokeratin and calretinin have the most value in differentiating different sarcomatoids. Clinicopathological data, especially information about the gross appearance of the tumor is quite important for sarcomatoid tumors. Thus, it should be noted and carefully correlated with microscopic and immunohistochemical findings.