Peritoneal Mesothelioma
Pain and abdominal distention with ascites are almost constant in patients with peritoneal mesothelioma. 63,182 Other clinical findings include nausea and vomiting, bowel obstruction, abdominal and pelvic masses, edema of the lower extremities, fever, hernia, hydrocele, and obstructive uropathy. Coexistent pleural effusion may occur. Direct biopsy by laparotomy or peritoneoscopy is the best diagnostic procedure. Ultrasonography and/or CT are useful techniques to follow the course of the disease and to visualize fluid and tumor masses.312 Median survival is about 10 months from onset of symptoms and 7 months from diagnosis.63
Paraneoplastic Syndromes
The most frequent paraneoplastic syndromes are hematologic. Among them thrombocytosis (platelet count above 400,000 per microliter) has been first observed by Chahinian and colleagues63 in about 40% of patients at diagnosis and in up to 90% of patients during the course of the disease, a finding which has been confirmed by others.187,225 It raises interesting questions about the reported role of platelet-derived growth factors (see above), and thrombocytosis has been linked to a poor prognosis.62,225,226 It has been suggested in a case of peritoneal mesothelioma that thrombocytosis was secondary to the large amounts of interleukin-6 (IL-6) produced by tumor cells,125 and this was confirmed in 25 patients with pleural mesothelioma.188b A full leukemoid reaction is much less common.
225 Other hematologic manifestations include clotting abnormalities (venous thrombosis, pulmonary emboli) not necessarily associated with thrombocytosis, as well as disseminated intravascular coagulation and autoimmune hemolytic anemias.13,225 Rare associations include the syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypoglycemia, and hypercalcemia.127,225 Recently, parathyroid hormone-like peptide has been identified in mesothelioma cells, as well as in normal and reactive mesothelial cells.175 Human chorionic gonadotropin (hCG) has been detected in ascites fluid and tumor cell lysate but not in the serum of a patient with malignant peritoneal mesothelioma and gynecomastia.209
Prognostic Factors
Performance status has been one of the most reliable prognostic factors, 10,63 in addition to the stage, which is discussed below with surgical CHAPTER 89 / Malignant Mesothelioma 1297 Figure 89.2. Malignant pleural mesothelioma, advanced stage. Marked thickening of the right pleura with tumor nodules and retraction of ipsilateral hemithorax. Basal predominance is well shown. No fluid was demonstrable by decubitus films.
Neoplasms of the Thorax making it the earliest abnormality, compared with other asbestosrelated pleural diseases, such as mesothelioma, pleural plaques, and pleural calcifications.95 Typically, the effusion resolves spontaneously, but ipsilateral relapses are frequent, and contralateral disease may appear.25,57 Almost two-thirds may be asymptomatic.95 Confusion with malignant mesothelioma is common in view of a history of asbestos exposure and a bloody pleural fluid in the majority of cases. Pleural biopsy shows dense fibrosis with scattered nonmalignant cells. Close follow-up is necessary, since some patients have developed malignant mesothelioma 6 to 12 years after such an episode.57,95
Mesothelioma is now a common cause of 'idiopathic" pleural effusion (Fig. 89.4). At the Mayo Clinic, it accounted for 8% (4 of 51) of all idiopathic pleural effusions and for 22% (4 of 18) of cases for which follow-up allowed a definite diagnosis.230 Some patients with malignant mesothelioma give a history of recurrent pleural effusion for years before the diagnosis is made. It is often impossible in retrospect to attribute such cases to a slow-growing mesothelioma or a prior benign asbestos effusion. The frequent difficulties of cytologic diagnosis and differentiation from reactive benign mesothelial proliferation, as discussed above, further compound this important clinical problem. Any suspicion added to a history of asbestos exposure warrants an aggressive diagnostic approach, including thoracoscopy or open biopsy, if necessary.
It is difficult to distinguish malignant mesothelioma from other carcinomas and sarcomas. Confusion with a peripheral adenocarcinoma of the lung metastatic to the pleura or with pancreatic, gastrointestinal, or ovarian adenocarcinoma metastatic to the peritoneum or pleura is frequent, not only on frozen sections but also on fixed paraffin sections. Specials stains and analyses of effusions for hyaluronic acid can be particularly useful in these circumstances. Pleural implantation can also occur in invasive thymomas or lymphomas, and desmoid tumors can invade the abdominal or chest walls.
Another difficult problem is to classify the so-called papillary tumors of the peritoneum in women in the absence of an obvious primary tumor such as ovarian serous carcinoma.137 Special stains for mucin are often negative and of little help. The exact nosologic classification of such tumors is still controversial. Different theories of histogenesis have led to various names, ranging from 'papillary carcinoma" arising from embryonic peritoneal nests of Mullerian tissue to 'ovarian mesothelioma" arising from the surface of the ovary.137,193,204
Asbestos exposure is uncommonly found. The course of such tumors appears more protracted than the real diffuse peritoneal mesothelioma, and prolonged survival for years after palliative surgery, and sometimes chemotherapy, is another distinguishing feature which makes recognition of this entity clinically important.79,204
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