Primary peritoneal epithelioid mesothelioma of clear cell type with a novel VHL gene mutation: a case report.

Clear cell variant of epithelioid mesothelioma is an extremely rare tumor with only isolated cases reported so far in the peritoneum. Here, we report a case of peritoneal epithelioid mesothelioma, clear cell variant, in a 63-year-old female patient with a novel VHL gene mutation and an unusual indolent clinical course. The patient, who has no clinical history of asbestos exposure, presented with a 27.2-cm upper abdominal mass and a 5.5-cm liver lesion. Retrospective review of the patient's abdominal computed tomographic scan 4 years ago showed 2 small abdominal lesions that were felt clinically to represent hemangiomas. These were retrospectively considered to have grown in size and represented the current abdominal mass. Both masses were subsequently biopsied and showed a proliferation of monomorphic epithelioid cells with distinct cell membranes, fine chromatin, and clear to finely vacuolated pale eosinophilic cytoplasm arranged in nests and solid sheets. Immunohistochemical staining confirmed it to be malignant mesothelioma. Clear cell variant of peritoneal epithelioid mesothelioma should always be considered in patients with an abdominal or pelvic mass with clear cell features. Given the rarity of such entity, its clinical course and prognosis remains unclear.