Peritoneal mesothelioma presenting as a skin nodule.

Mesothelioma is a malignancy of the pleura, pericardium and peritoneum that is rarely seen in cutaneous biopsies. We present a case of a 75-year-old man with significant occupational exposure to asbestos who developed peritoneal mesothelioma that presented as a skin nodule in an old appendectomy scar. The patient presented with a complaint of increased hardness along his appendectomy scar. Physical examination revealed an anterior abdominal wall mass overlying the appendectomy scar, which was subsequently biopsied. Histologic examination of the abdominal wall mass revealed an infiltrating epithelioid and papillary neoplasm within the dermis and subcutaneous tissue. Immunohistochemical stains showed immunoreactivity for cytokeratin (CK) 7, CK 5/6, calretinin and vimentin. CK 20, monoclonal carcinoembryonic antigen, prostate-specific antigen and prostate-specific acid phosphatase were negative. The profile supported the diagnosis of mesothelioma. Cutaneous presentation of mesothelioma is rare but should be considered in the differential diagnosis of patients with significant asbestos exposure.