What are the different types of mesothelioma?

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Pleural, Peritoneal, Pericardial

Pleural mesothelioma

Pleural mesothelioma is of two kinds: (1) diffuse and malignant (cancerous), and (2) localized and benign (non-cancerous.)

Benign mesotheliomas can often be removed surgically, are generally not life-threatening, and are not usually related to asbestos exposure. Malignant mesotheliomas, however, are very serious. Fortunately, they are rare – about two thousand people are diagnosed with mesothelioma in the U.S. each year.

The remainder of this section is about diffuse malignant pleural mesothelioma.

Pleural mesothelioma is a cancer of the cells that make up the pleura or lining around the outside of the lungs and inside of the ribs. Its only known cause in the U.S. is previous exposure to asbestos fibers, including chrysotile, amosite or crocidolite. This exposure is likely to have happened twenty or more years before the disease becomes evident, since it takes many years for the disease to “incubate.” It is the most common type of mesothelioma, accounting for about 75% of all cases.

Mesothelioma is sometimes diagnosed by coincidence, before there are any symptoms. For instance, tumors have been discovered through routine chest x-rays. However, when symptoms occur, they may include shortness of breath, weakness, weight loss, loss of appetite, chest pains, lower back pains, persistent coughing, difficulty in swallowing, alone or in combination. An initial medical examination often shows a pleural effusion, which means an accumulation of fluid in the pleural space – the area between the lungs and the chest wall.

The first step in detecting pleural mesothelioma is, typically, a chest x-ray or CT scan. This is often followed by a bronchoscopy, using a viewing scope to look inside the lungs.

The actual diagnosis usually requires obtaining a piece of tissue through a biopsy. This could be a needle biopsy, an open biopsy, or through a tube with a camera (thoracoscopy or chest scope.) If an abnormality is seen through the camera then a tissue sample can be taken at the same time, using the same tube. This is a hospital procedure that requires anesthesia, but is not usually painful. The tissue sample is tested by a pathologist.

Fluid build-up from the pleural effusion can generally be seen on a chest x-ray and heard during a physical examination, but a firm diagnosis of mesothelioma can only be made through a biopsy and pathological testing. This is important because there are also benign pleural effusions and other tumors that have a similar appearance to mesothelioma. Diagnosing mesothelioma can be quite difficult; it requires special lab stains, and much experience in understanding them.

The spread of the tumor over the pleura causes pleural thickening. This can reduce the flexibility of the pleura and encase the lungs in an increasingly restrictive girdle. With the lungs restricted, they get smaller and less functional, and breathing becomes more difficult. At first a person with mesothelioma may be breathless only when he or she exercises, but as lung function drops, he or she can become short of breath even while resting.

The tumor spreads by direct invasion of surrounding tissue. As it spreads inward it can compress the lungs. As the tumor spreads outward it can invade the chest wall and ribs, and this can be extremely painful.

Current medical science does not know exactly how and why, at a cellular level, asbestos fibers cause mesothelial cells to become abnormal (malignant or cancerous.) Thus it is not known whether only one fiber causes the tumor or whether it takes many fibers. It seems that asbestos fibers in the pleura can start a tumor as well as promote its growth; the tumor does not depend on any other processes for its development.

There is as yet no known cure for malignant mesothelioma. The prognosis depends on various factors, including the size and stage of the tumor, the extent of the tumor, the cell type, and whether or not the tumor responds to treatment. KMESA has represented many clients who lived for five to ten years after diagnosis, most of them in good health for a majority of those years. Some mesothelioma victims succumb within a few months; the average survival time is about a year.

The treatment options for people with mesothelioma have improved significantly, especially for those whose cancer is diagnosed early and treated vigorously. Many people are treated with a combination of therapies, sometimes known as multimodal therapy.

Specific types of treatment include:

  • Chemotherapy and other drug-based therapies
  • Radiation therapy
  • Surgery and
  • Intra-operative photodynamic therapy.

There are also experimental treatments like gene therapy and immunotherapy, angiogenesis inhibitors, and clinical trials for various new treatments and combinations of treatments.

Treatments that reduce pain and improve lung function, are becoming more successful (although they cannot cure mesothelioma.) Pain control medications have become easier to administer. Debulking is a surgical process of removing a substantial part of the tumor and reducing the pleural thickening; this can provide significant relief. X-ray therapy has also been successfully used to control the tumor and the pain associated with it for a while.

Peritoneal Mesothelioma

Many of the organs in the abdomen are enveloped by a thin membrane of mesothelial cells, known as the peritoneum.

Peritoneal mesothelioma is a tumor of this membrane. Its only known cause in the U.S. is previous exposure to asbestos, but it can be many years after exposure before the disease appears. Peritoneal mesotheliomas account for about one-fifth of all mesotheliomas.

Like pleural mesothelioma, peritoneal mesothelioma can be either benign or malignant. This discussion is only about malignant peritoneal mesothelioma.

Mesothelioma is sometimes diagnosed by coincidence, before any symptoms have appeared. For example, the tumor is sometimes seen on a routine abdominal x-ray for a check-up or before surgery.

When the symptoms of peritoneal mesothelioma appear, they typically include abdominal pains, weakness, weight loss, loss of appetite, nausea, and abdominal swelling. Fluid often accumulates in the peritoneal space, a condition known as ascites. Over time the wasting symptoms can become more and more severe.

The growing tumor can exert increasing pressure on the organs in the abdomen, leading to bowel obstruction and distention. If the tumor presses upward, it can impair breathing capacity. If the tumor pushes against areas with many nerve fibers, and the bowel distends, the amount of pain can increase.

X-rays and CT scans are, typically, the first step towards detecting peritoneal mesothelioma. The actual diagnosis is typically achieved by obtaining a piece of tissue. The medical procedure of looking at the peritoneum is known as a peritoneoscopy. It is a hospital procedure and requires anesthesia. If an abnormality is seen, the doctor will attempt to obtain a tissue sample – this is known as a biopsy. The tissue sample will be examined by a pathologist who makes a diagnosis using microscopic analysis of specialized stains.

There are at least two explanations for how asbestos fibers can get into the peritoneum. The first is that fibers caught by the mucus of the trachea and bronchi end up being swallowed. Some of them lodge in the intestinal tract and from there they can move through the intestinal wall into the peritoneum. The second explanation is that fibers that lodge in the lungs can move into the lymphatic system and be transported to the peritoneum.

Medical science does not know exactly how or why, at a cellular level, a carcinogen like asbestos causes a cell to become malignant (cancerous.) Thus it is not known whether only one fiber can cause a tumor to develop or whether it takes many fibers, or what the exact conditions and predispositions are for this change to happen.

At this time there are treatments, but no known cure, for peritoneal mesothelioma. The prognosis depends on various factors, including the size and stage of the tumor, its extent, the cell type, and whether or not the tumor responds to treatment.

Benign Mesothelioma

A rare form of mesothelioma is the cycstic mesothelioma of the peritoneum. Its prognosis is benign. Its occurrence has been described primarily in young women. However the diagnosis presents difficulties, requiring extensive electron miscroscopy and immunohistochemical studies.

Rare Sites

Mesothelioma of the pericardium, is a very seldom seen cardiac cancer. The mass is usually detected at a late stage by echocardiography, the prognosis is very poor , with or without therapy. Mesothelioma of the ovaries and the scrotum have also been reported in the literature. The management differs based on the stage of the disease, the prognosis is also very poor. The etiology of the few cases of mesothelioma described in children remains unclear and is not believed to be asbestos-related, the therapy and prognosis differ on an individual basis.

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