The White Lung Association

Malignant mesothelioma is a rare type of cancer that affects the mesothelium cells (cells that compose the exterior lining of body cavities). Most commonly, mesothelioma affects the pleural cavity (chest cavity that encapsulates the lungs) and peritoneal cavity (abdominal cavity). However, the illness has also been known to manifest in the pericardium, which lines the heart.

Mesothelioma is a fatal illness. Once diagnosed, average survival rate for patients is approximately 12 months. In more than 90 percent of all cases, mesothelioma is a direct result of asbestos exposure. Asbestos is a naturally occurring fiber that is used in a variety of insulation and flame-retardant products.

Who Gets Mesothelioma?

Mesothelioma is most common among individuals between the ages of 50 and 70. This is largely because the illness typically does not manifest until decades after initial asbestos exposure. In some cases, mesothelioma may not be diagnosed until 50 years after inhalation. Mesothelioma is rarely diagnosed among children. For those diagnosed between the ages of 20 and 40, childhood asbestos exposure is typically the cause.

Approximately 70 to 80 percent of all mesothelioma cases involve a male patient. This is due to the fact that men are more likely to be employed at jobs that have a heightened risk for asbestos exposure. Common industries linked to asbestos inhalation include construction, auto repair, shipbuilding and naval employment.

Malignant Mesothelioma Symptoms

A number of symptoms have been linked to malignant mesothelioma. Two of the most common symptoms are chest pain and dyspnoea. Dyspnoea is the clinical term for shortness of breath. These two symptoms may be exhibited simultaneously in a patient. However, about one-third of all patients displayed shortness of breath in the absence of chest pain.

Dysphagia (difficulty swallowing) is another common symptom linked to mesothelioma. Less common symptoms of the illness include weight loss, sweating and a chest wall mass. For peritoneal-specific cases of mesothelioma, loss of appetite, vomiting, nausea, and bowel issues may also be indicators of the disease.

The underlying cause of most symptoms associated with malignant mesothelioma is pleural effusion. Pleural effusion is defined as the buildup of fluid within the layers that line the lungs and chest cavity. For peritoneal mesothelioma, ascites may also occur. Ascites is the buildup of excess fluid in the abdominal cavity.

How Mesothelioma Forms and Spreads

Scarring of the lung tissue causes mesothelioma. This is almost always the result of inhaled asbestos fibers, which become lodged in the lung walls. Over time, these fibers aggravate the lung tissue and eventually cause scarring. This generally leads to the formation of a tumor on the lining of the abdominal cavity (parietal pleura). Cancerous cells then spread via fissures in the lining until the entire lung surface is encapsulated.

Mesothelioma can also manifest along needle tracks and incisions. If the illness spreads to the lining of the heart, then cardiac tamponade (fluid buildup in the heart cavity) may lead to compression of the organ.

Diagnosing Mesothelioma

Malignant mesothelioma can be difficult to diagnose. This is partly due to the fact that expressed symptoms of the disease are common among many other illnesses. However, a physical examination may result in the identification of pleural effusion or pleural thickening as a result of the tumor. Blood tests can also serve as early indicators to the disease. If blood tests reveal an elevated erythrocyte sedimentation rate (ESR), then mesothelioma may be identified as a possible cause. ESR refers to the precipitation rate of red blood cells. Elevated rates indicate inflammation in the body.

Once mesothelioma is suspected, a CT scan, MRI and/or PET scan may be ordered in the attempt to identify a mesothelioma tumor. However, to properly diagnose mesothelioma, a biopsy is required. This involves extracting a small tissue sample from the affected area and viewing it under a microscope.

Types of Mesothelioma

For a mesothelioma biopsy, doctors look for one of three types of cancerous cells: epithelioid, sarcomatoid or biphasic. Epithelioid mesothelioma is the most common form of the illness, accounting for 50 to 70 percent of all diagnosed cases. Epithelioid cells exhibit a tubular pattern, uniform shape and a defined cell nucleus.

Sarcomatoid mesothelioma is the least common form of the illness, comprising approximately 10 to 15 percent of all cases. Sarcomatoid cells are more irregular and oval in shape than epithelioid cells, and also exhibit a less defined cell nucleus.

Biphasic mesothelioma accounts for 20 to 40 percent of all mesothelioma cases. In this form of mesothelioma, both epithelioid and sarcomatoid cancer cells are present.

Complications of a Mesothelioma Diagnosis

The successful diagnostic rate from CT-guided biopsies is estimated at 60 percent. Due to this fact, multiple biopsies may be taken, which can improve successful diagnostic rate to about 85 percent. For better results, more invasive procedures such as open pleural biopsy may be required. This involves opening the chest cavity via incision to extract a biopsy.

However, diagnosis is further complicated by the fact that mesothelioma acts remarkably similar to other forms of cancer. For example, epithelioid mesothelioma cells are often confused for adenocarcinoma cells, and vice versa. As such, additional diagnostic procedures may be necessary.

Though no current diagnosis procedure provides 100 percent effectiveness, searching for several biological markers of the illness generally leads to a correct diagnosis.

For such purposes, doctors and researchers have had some success by checking for elevated protein markers associated with mesothelioma, such as mesothelin, cytokeratin 5/6, cairetinin, thrombomodulin and WT-1. Still, these markers may also be present in other types of cancer, though to a lesser extent. As such, a positive or negative identification of two markers generally is enough to warrant a confirmation of mesothelioma.

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