Here, tumor is composed of nests and sheets of polygonal, epithelial cells. Nuclei have mild pleomorphism and small nucleoli. This tumor shows glands and papillary structures, resembling adenocarcinoma. This tumor is composed of spindled cells and some collagenous stroma. The nuclei have irregular shapes.
Lymphocytes surround a vessel near the bottom.
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.