Myxoid variant of peritoneal epithelioid malignant mesothelioma. A case report

The myxoid variant of a diffuse malignant epithelioid mesothelioma is a rare tumor. To the best of our knowledge, only three cases of this type of mesothelioma involving the peritoneum have been reported in the literature to date. Although it is rare in the peritoneal cavity, it should be included in the differential diagnosis of the more common myxoid/mucinous abdominal lesions (e.g. mucinous carcinomas or pseudomyxoma peritonei), which can myxoid MM mimic. We report the case of a 60-year-old female with a myxoid variant of malignant peritoneal mesothelioma. Histologically, the tumor consisted of medium-sized to large epithelioid cells with a moderate to abundant amount of eosinophilic cytoplasm. Some of the tumor cells contained intracytoplasmic, optically clear vacuoles. The nuclei were irregular with coarse chromatin and some exhibited prominent nucleoli. Some of the cells were multinucleated. Mitotic figures were rare. Most of the tumor cells were located within an ample myxoid background. Immunohistochemically, the tumor cells showed a diffuse positivity for cytokeratin cocktail AE1/AE3, calretinin, D2-40, and cytokeratin 7. Vimentin, HBME-1 and WT-1 were only focally positive. Progesterone receptors showed positivity in rare tumor cells (up to 5%). Other markers examined, including cytokeratin 20, estrogen receptors, BerEP4, CEA, TTF-1, GCDFP-15, and CD15 were negative.