The differential diagnosis includes other sarcomas. For sarcomatous tumors, a positive stain for keratin supports a diagnosis of mesothelioma. More recently, the calretinin stain has been employed as a marker for mesothelial cells, either epithelial or sarcomatous. Usually several stains are employed in a particular case. Ultrastructural features also help to distinguish carcinoma from mesothelioma.
Carcinomas typically have few, short, non-branched microvilli.
Note branch at arrow.