Deciduoid mesothelioma: a rare, distinct entity with unusual features.

An unusual case of deciduoid mesothelioma occurring in the anterior abdominal wall of a 30-year-old woman is reported. The patient had a palpable mass that was resected. The mass appeared largely cystic with solid areas. Histologically, the tumor cells appeared epitheloid with eosinophilic cytoplasm and prominent nucleoli. The tumor was positive for keratins and vimentin and negative for CEA and Ber-EP4. Electron microscopy showed features of mesothelial cells characterized by well-formed desmosomes and long, slender microvilli. In contrast to previously reported cases of deciduoid mesothelioma, this tumor developed in the abdominal wall and appears to have a benign course.