Multicystic mesothelioma. An analysis of pathologic findings and biologic behavior in 37 cases.

We report the clinicopathologic findings of 37 cases of multicystic mesothelioma. The tumor, which occurs most frequently in young to middle-aged women, affects chiefly the pelvic peritoneum--particularly the cul de sac, uterus, and rectum. It grows along the serosa as multiple, translucent, fluid-filled cysts. Occasionally, it manifests as a solitary or free-floating mass. The tumor is made up of mesothelial-lined cysts embedded in a delicate fibrovascular stroma. The mesothelial cells may be flattened or cuboidal. Adenomatoid change or squamous metaplasia of the mesothelium occurs in one-third of cases. In a significant percentage of cases, the stroma shows marked inflammatory changes that make it difficult to recognize the underlying neoplastic nature. Follow-up information in 25 patients showed that 21 patients were alive, two had died of tumor, and two died of other causes. One of the two patients who died of their tumors was an infant whose tumor showed transition to conventional mesothelioma; the other was a man who had refused therapy. The extent of tumor at the time of diagnosis did not predict survival. The low incidence of previous surgery, the lack of prior abdominal infections, and the documentation of disease-related mortality all support a neoplastic, rather than a reactive, basis for this lesion.