Peritoneal Mesothelioma

A rare type of tumor arising from the peritoneum

Peritoneal Mesothelioma

The peritoneum cavity lines all the organs of the abdominal cavity and lubricates them, permitting their smooth movement. It has immunological functions also. Malignant peritoneal mesothelioma is a rare type of tumor arising from the peritoneum itself.

Peritoneal mesothelioma form plaque-like deposits on the visceral and parietal peritoneum which can range in size from a few millimeters 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.

The Causes?

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 are 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.

Types of Mesothelioma

10-20% of the mesotheliomas arise from the peritoneum. Peritoneal mesotheliomas can be malignant or non-malignant. Malignant peritoneal mesotheliomas have 3 common subtypes or varieties: the Epithelial, Sarcomatoid and Biphasic varieties.
Epithelial mesothelioma occurs in 50 to 70 percent of the cases and is the most common type of peritoneal mesothelioma. It also has the best outcome and longest survival among the three most common varieties.

Sarcomatoid mesothelioma occurs in 7 to 20 percent of the cases, while Biphasic occurs in approximately 20 to 35 percent.

The other rare subtypes are : multicystic peritoneal mesothelioma (non-malignant) and well-differentiated papillary mesothelioma and mesothelioma expressing mucin (both of which are subtypes of epithelioid mesothelioma).

Symptoms & Diagnosis

The symptoms of mesothelioma are swelling of the abdomen, pain, loss of appetite, weight loss along with other 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 a final diagnosis is made. Diagnostic procedures involve extraction of fluid from the peritoneum for lab testing. The fluid and tissue samples are 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.

The Treatment

The most effective therapy for peritoneal mesothelioma is cytoreductive surgery and HIPEC. 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 may be 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 Cytoreduction is CC-0 – Partial with a diameter of the residual nodules < 0.25 cm is CC -1 – Nodules between 0.25 to 2.5 cm is CC-2 – Nodules > 2.5 cm or confluence of tumor nodules is 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 information 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. Mesotheliomas are generally considered a fatal neoplasm, and until CRS and HIPEC was used for its treatment, the average survival was only 1 year. With CRS and HIPEC, a large percentage of the patients may survive for 5 years or more. 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.