All About Mesothelioma from CNN Health Library

Mesothelioma
From MayoClinic.com Special to CNN.com

Introduction
Malignant mesothelioma is a rare cancer that occurs in the thin layer of tissue that covers the majority of your internal organs (mesothelium). Doctors divide mesothelioma into different categories based on what part of the mesothelium is affected by cancer. Mesothelioma that occurs in the tissue that surrounds the lung (pleura) is called pleural mesothelioma and is the most common form. Mesothelioma that occurs in the tissue in your abdomen (peritoneum) is called peritoneal mesothelioma and accounts for 10 percent to 20 percent of all mesotheliomas. In rare cases, mesothelioma can also occur in the lining around the heart (pericardium) and in the lining around the testicles (tunica vaginalis).

Between 2,000 and 3,000 people are diagnosed with mesothelioma in the United States each year. Men are more likely to develop mesothelioma than are women. It's more common in older adults — most people with mesothelioma are 65 and older — though mesothelioma can be diagnosed at any age.

Mesothelioma is closely linked to exposure to asbestos — a natural fiber that was once used in manufacturing a wide variety of industrial and household products. Mesothelioma rates have increased during the past 20 years in response to the widespread use of asbestos in the past. Many industrialized countries now limit asbestos use and enforce laws to protect workers who may be exposed. Researchers predict these efforts will lead to fewer cases of mesothelioma in the future.

Signs and symptoms
Signs and symptoms of mesothelioma vary depending on where the cancer occurs.

Pleural mesothelioma signs and symptoms may include:
Shortness of breath
Painful breathing
Chest pain under the rib cage
Unusual lumps of tissue under the skin on your chest
Unexplained weight loss
Dry (nonproductive) cough

Peritoneal mesothelioma signs and symptoms may include:
Abdominal pain
Abdominal swelling
A change in your bowel habits, such as more frequent diarrhea or constipation
Lumps of tissue in the abdomen
Unexplained weight loss

Signs and symptoms of pericardial mesothelioma and mesothelioma of the tunica vaginalis are unclear. These forms are so rare that not much information is available. Mesothelioma of the tunica vaginalis may be first detected as a mass on a testicle. Pericardial mesothelioma signs and symptoms may include difficulty breathing and fever.

Signs and symptoms of mesothelioma that has spread to other parts of the body include:

Pain in the area where cancer has spread
Difficulty swallowing
Swelling in the neck and face


Causes
In general, cancer begins with a genetic mutation that turns normal, healthy cells into abnormal cells. Healthy cells grow and multiply at a set rate, eventually dying at a set time. Abnormal cells grow and multiply out of control, and they don't die. The accumulating abnormal cells form a mass (tumor). Cancer cells invade nearby tissues and can break off from an initial tumor to spread elsewhere in the body (metastasize).

It isn't clear what causes the initial genetic mutation that leads to mesothelioma, though researchers have identified factors that may increase the risk. It's likely that cancers form because of an interaction between many factors, such as inherited conditions, your environment, your health conditions and your lifestyle choices.

Risk factors

Asbestos exposure plays a role in 70 percent to 80 percent of mesothelioma cases, though the actual percentage could be higher. Asbestos is a mineral that is found naturally in the environment. Asbestos fibers are strong and resistant to heat, making them useful in a wide variety of applications. Asbestos fibers have been used to make insulation, cement, brakes, shingles, flooring and many other products.

People who work around asbestos fibers are thought to have the greatest risk of mesothelioma. When asbestos is broken up — for instance, in the mining process or in removing asbestos insulation from a building — dust may be created. If the dust is inhaled or swallowed, the asbestos fibers may settle in the lungs or in the stomach, where they can cause irritation that may lead to mesothelioma, though how exactly this happens isn't understood. Although asbestos is still used in a limited number of industries, the federal government limits the amount of asbestos fibers workers may be exposed to and sets rules to protect workers.

Mesothelioma risk is believed to be increased in people who are exposed to high levels of asbestos, in people who are exposed to asbestos over a long period of time and in people exposed to asbestos at a young age. It can take 30 to 40 years or more for mesothelioma to develop as a result of asbestos exposure.

People who live with workers exposed to asbestos may also have an increased risk of mesothelioma. Asbestos dust is thought to have been carried home on workers' clothes. Today workers are required to shower and change clothes after working with asbestos to protect their families.

Some people with years of asbestos exposure never develop mesothelioma. Researchers estimate only about 5 percent of the people with the highest exposure to asbestos will develop mesothelioma. And yet, others with very brief exposure develop the disease. This indicates that other factors may be involved in determining whether someone gets mesothelioma or doesn't. For instance, you could inherit a predisposition to cancer or some other condition could increase your risk. Risk of mesothelioma is increased greatly in smokers who are exposed to asbestos.

Other possible risk factors

Researchers have identified other factors that may increase the risk of mesothelioma, including:

SV40. Some research indicates a link between mesothelioma and simian virus 40 (SV40), a virus originally found in monkeys. Millions of people may have been exposed to SV40 when receiving polio vaccinations between 1955 and 1963, because the vaccine was developed using monkey cells. Once it was discovered that SV40 was linked to certain cancers, the virus was removed from the polio vaccine. There is some evidence that SV40 may also be passed between people, though it isn't clear how. Whether SV40 increases the risk of mesothelioma is a point of contention, and more research is needed.

Radiation. The radioactive substance thorium dioxide was used along with X-rays to diagnose various health conditions from the 1920s to the 1950s. Thorium dioxide was later found to cause cancer and was no longer used. Some research links thorium dioxide to mesothelioma.

Asbestos-like minerals. A naturally occurring asbestos-like mineral called zeolite has been linked to mesothelioma cases in Turkey, where the mineral is used to construct homes.

Family history. Research into the same region of Turkey where zeolite is used reveals that family history may play a role in mesothelioma there. More research is needed to determine whether family history may predispose some people to mesothelioma.


Source:http://www.cnn.com/HEALTH/library/DS/00779.html