Malignant Peritoneal Mesothelioma
Malignant peritoneal mesothelioma is a rare type of tumor arising from the peritoneum itself. The peritoneum lines all the organs of the abdominal cavity and lubricates them and permits their smooth movement. It has immunological functions also.
Figure 1: Peritoneal deposits typically seen in Mesothelioma
What Causes Peritoneal Mesothelioma?
Peritoneal mesothelioma is known only to be caused by exposure to asbestos, a natural fiber that is used heavily in industry and at building construction sites. Asbestos is said to reach the abdominal wall by one of two methods. The first is through ingested asbestos fibers which are processed through digestion and become lodged in the peritoneum. The other method is through the lungs and lymph nodes, by inhaled asbestos fibers. Malignant mesothelioma of the pleura is also known to metastasize directly into the abdominal cavity if its spread is not slowed. It may take 20-50 years after asbestos exposure for a mesothelioma to develop
Spread of Peritoenal Mesothelioma
Peritoneal mesothelioma form plaque like deposits on the visceral and parietal peritoneum which can range in size from few mm to several centimeters. Due to this there is decreased absorption of peritoneal fluid leading to its accumulation and thus swelling of the abdomen. The movement of the intestines may be affected or they may get partially or completely blocked.
Mesotheliomas usually remain confined to the peritoneum and continue to grow within the cavity, however they may spread to the pleural cavity (pleura is the membrane covering the lungs) or to the glands in the abdomen and the chest.
Symptoms and Diagnosis
The symptoms of mesothelioma are distension of the abdomen, pain, loss of appetite, weight loss, symptoms of intestinal blockade. A doctor may suspect it if there is unusual persistence of abdominal or chest pain. Suspicious hernias may actually be a peritoneal effusion caused by peritoneal tumor growth. Misdiagnosis is common and it is not unusual for patients to undergo multiple imaging scans and a diagnostic biopsy before an official diagnosis is made.
Diagnostic procedures in which fluid is extracted from the peritoneum for lab testing are the only way to conclusively diagnose peritoneal mesothelioma. Samples will be examined for the presence of malignant cells. Once malignant cells are detected, further testing will be needed to classify these cells as malignant mesothelioma. For this IHC (immunohistochemistry) is done to confirm the mesothelioma and distinguish it from other peritoneal tumors.
Types of Mesothelioma
Mesotheliomas have 3 subtypes : epithelial, sarcomatoid and biphasic.
Epithelial mesothelioma occurs in 50 to 70 percent of most cases and is the most common cell type. Sarcomatoid mesothelioma occurs in 7 to 20 percent of cases, while biphasic occurs in approximately 20 to 35 percent.
The other rare subtypes are : adenoid cystic, tubulopapillary, glandular, histiocytoid, microcystic, macrocystic, signet ring, single file, diffuse — NOS, glomeruloid, poorly differentiated (large cell) or pleomorphic, mucin positive, gaucher cell-like, in situ and well-differentiated papillary.
Cytoreductive Surgery and HIPEC
For patients with confirmed MPM, radical resection (Cytoreductive surgery) is associated with improvement in survival and is attempted whenever possible. Once again the outcome depends on the ability of the surgeon to remove all the tumor. When complete removal of the tumor is achieved, HIPEC is performed. If the tumor is extensive, it maybe impossible for the surgeon to achieve this.
After surgical debulking, the resection can be classified according to the Completeness of Cytoreduction Score, which evaluates the residual peritoneal seeding within the operative field: complete (CC-0) or partial with a diameter of the residual nodules < 0.25 cm (CC-1), 0.25-2.5 cm (CC-2), > 2.5 cm or confluence of tumor nodules (CC-3). The CC-1 tumor nodule size is thought to be penetrable by intracavitary chemotherapy and is, therefore, designated as complete cytoreduction if perioperative intraperitoneal chemotherapy is used. The limitation of this score is the fact that it can be evaluated only after surgery; therefore, no preoperative informations can be obtained about the resectability of the tumor. Survival after cytoreductive surgery and intraperitoneal chemotherapy is 35.8 months for patients treated with a CC-0 or CC-1 resection, and only 6.5 months for those treated with a CC-2 or CC-3 resection.
When surgery is not feasible or the tumor resection is incomplete, systemic chemotherapy is given with the goal of controlling the disease. But the outcomes are generally poor and do not compare with surgery Prognosis and outcome
Mesotheliomas are generally considered a fatal neoplasm, and until CRS and HIPEC was used for its treatment, the overall median survival was only 1 year. With CRS and HIPEC, a large percentage of the patients may survive for 5 years or more. Tumor histology, previous surgical score, lesion size, distribution (assessed with Gilly classification and peritoneal cancer index), and completeness of cytoreduction score are the main prognostic index.