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 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

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.

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.

See your doctor if you have signs and symptoms that may indicate mesothelioma. Signs and symptoms of mesothelioma aren't specific to this disease and may be related to other conditions. If any signs and symptoms seem unusual or bothersome to you, ask your doctor to check them out.

If you have signs and symptoms that might indicate mesothelioma, your doctor will conduct a physical exam, paying particular attention to areas where you're experiencing pain. He or she checks for any lumps or other unusual signs. Your doctor may order other tests to determine the cause of your signs and symptoms, including:

• Chest X-ray. X-rays may show abnormalities if you have pleural mesothelioma.
• Chest or abdominal CT scan. Computerized tomography (CT) may reveal abnormalities in your chest or abdomen if you have mesothelioma.

It's not uncommon for mesothelioma to be misdiagnosed initially because mesothelioma is rare and its signs and symptoms aren't specific. Your doctor will likely rule out other more common conditions before considering mesothelioma.

Biopsy
Biopsy, a surgical procedure to remove a small portion of the mesothelium for laboratory examination, is the only way to determine whether you have mesothelioma. Depending on what area of your body is affected, your doctor selects the right biopsy procedure for you. Options include:

• Fine-needle aspiration. The doctor removes fluid or a piece of tissue with a small needle inserted into your chest or abdomen.
• Thoracoscopy. Thoracoscopy allows the surgeon to see inside your chest. In this procedure, the surgeon makes one or more small incisions between your ribs. He or she inserts a tube with a tiny video camera to see inside your chest cavity — a procedure sometimes called video-assisted thoracoscopic surgery (VATS). Special surgical tools allow your surgeon to cut away a piece of tissue.
• Laparoscopy. Laparoscopy allows the surgeon to see inside your abdomen. Using one or more incisions into your abdomen, the surgeon inserts a tiny camera and special surgical tools to obtain a small piece of tissue for examination.
• Thoracotomy. Thoracotomy is surgery to open your chest to allow a surgeon to check for signs of disease. He or she removes a sample of tissue for testing.
• Laparotomy. Laparotomy is surgery to open your abdomen to allow a surgeon to check for signs of disease. He or she removes a sample of tissue for testing.

Once the tissue sample has been collected through biopsy, the sample is analyzed under a microscope. This determines whether or not the abnormal tissue is mesothelioma. Biopsy samples also allow your doctor to test for the type of cells involved in your mesothelioma. The type of mesothelioma you have is used to determine your treatment plan.

Staging
Once mesothelioma is diagnosed, your doctor orders other tests to determine the extent of the cancer and whether it has spread — a process called staging. Imaging procedures allow doctors to see inside your chest or abdomen to determine the stage of mesothelioma. Options include:

• Chest X-ray
• CT scans of the chest and abdomen
• Magnetic resonance imaging (MRI)
• Positron emission tomography (PET)

Once the extent of mesothelioma is determined, a stage is assigned. Staging helps your doctor determine your prognosis and the best treatment plan. The stages of mesothelioma are:

• I. Stage I mesothelioma is considered localized cancer, meaning it's limited to one small area of the chest or abdomen.
• II. Stage II mesothelioma is considered advanced cancer. Mesothelioma at this stage involves the mesothelium and has also spread to other structures directly adjacent to the tumor, such as the lungs or the diaphragm.
• III. Stage III mesothelioma is also considered advanced cancer. Mesothelioma at this stage meets the same requirements as stage II, but has also spread to the lymph nodes in the region.
• IV. Stage IV mesothelioma is an advanced cancer that has spread to distant areas (metastasized). Mesothelioma most commonly spreads (metastasizes) to the brain and areas of the lung that are away from the tumor.

As pleural mesothelioma spreads in the chest, it puts pressure on the structures in that area. This can cause complications, such as:

• Difficulty breathing
• Chest pain
• Difficulty swallowing
• Swelling caused by pressure on the large vein that leads from your upper body to your heart (superior vena cava syndrome)
• Pain caused by pressure on the nerves and spinal cord

Mesothelioma that progresses can lead to death. People who die of mesothelioma usually die from related complications, such as lung failure, bowel obstruction, heart problems, stroke and other causes.

What treatment you undergo for mesothelioma depends on your health and certain aspects of your cancer, such as its stage and location. Unfortunately, mesothelioma often is an aggressive disease and for many people a cure won't be possible. Mesothelioma is usually diagnosed at an advanced stage — when it isn't possible to remove the cancer through surgery. Instead, your doctor may work to control your cancer and its signs and symptoms to make you more comfortable.

Discuss your treatment goals with your doctor. Some people want to do everything they can to treat their cancer, even if that means enduring side effects for a small chance of a cure. Others prefer treatments that make them comfortable so that they can live their remaining months as symptom-free as possible.

Mesothelioma treatment options may include surgery, radiation, chemotherapy and clinical trials.

Surgery
Surgeons work to remove mesothelioma from your body. Sometimes it isn't possible to remove all of the cancer. In those cases, surgery may help to reduce the signs and symptoms caused by mesothelioma spreading in your body. Surgical options may include:

• Surgery to decrease fluid buildup. Pleural mesothelioma may cause fluid to build up in your chest, causing difficulty breathing. Surgeons insert a tube or catheter into your chest to drain the fluid. Surgeons may also inject medicine into your chest to prevent fluid from returning (pleurodesis).
• Surgery to remove the tissue around the lung or abdomen. Surgeons may use scalpels and other surgical tools to remove the tissue lining the ribs and the lungs (pleurectomy) or the tissue lining the abdominal cavity (peritonectomy) in order to relieve signs and symptoms of mesothelioma.
• Surgery to remove as much of the cancer as possible (debulking). If all of the cancer can't be removed, surgeons may attempt to remove as much as possible.
• Surgery to remove a lung and the surrounding tissue. Removing the affected lung and the tissue that surrounds it may relieve signs and symptoms of pleural mesothelioma. This procedure also allows doctors to use higher doses of radiation against any remaining mesothelioma, since doctors won't need to worry about protecting your lung from damaging radiation.

Chemotherapy
Chemotherapy uses chemicals to kill cancer cells. Chemotherapy drugs travel throughout your body and kill rapidly growing cells. This works against cancer cells, but also affects other rapidly growing cells in your body, such as those in your hair follicles and those in your gastrointestinal system. Chemotherapy may slow the growth of pleural mesothelioma. Chemotherapy can be used before surgery (neoadjuvant chemotherapy) or after surgery (adjuvant chemotherapy) to reduce the signs and symptoms you may experience from mesothelioma.

People with peritoneal mesothelioma may receive adjuvant chemotherapy drugs that have been heated (hyperthermic chemotherapy). Rather than being distributed throughout the body, chemotherapy drugs are often injected directly into the abdominal cavity (intraperitoneal chemotherapy), where they can reach the peritoneal mesothelioma directly without injuring healthy cells in other parts of the body. This allows doctors to administer higher doses of chemotherapy drugs. Intraperitoneal chemotherapy may also be used to reduce the signs and symptoms of peritoneal mesothelioma that can't be removed through surgery.

Radiation therapy
Radiation therapy focuses high-energy radiation to a specific spot or spots on your body. Radiation may reduce signs and symptoms in people with pleural mesothelioma. Doctors aim radiation at the entire chest to obtain the best result. However, many sensitive organs reside in the chest, such as the heart, lungs and spinal cord, so doctors must use low doses of radiation to spare these organs. Radiation therapy is sometimes used after biopsy or surgery to prevent mesothelioma from spreading to the surgical incision.

Radiation therapy is used occasionally in people with peritoneal mesothelioma. Radiation may reduce signs and symptoms of mesothelioma.

Combination therapy
Surgery, chemotherapy and radiation therapy may be combined. This aggressive therapy can be grueling and may not be appropriate for everyone. Younger, healthier people and those with earlier stage mesothelioma may be more able to endure this treatment. Combination therapy has shown the most promise in treating mesothelioma. However, most people will eventually experience a recurrence of this cancer despite this aggressive treatment. Combination therapy has been used in both pleural mesothelioma and peritoneal mesothelioma.

Clinical trials
Clinical trials are studies of new mesothelioma treatment methods. People with mesothelioma may opt for a clinical trial for a chance to try new types of treatment. However, a cure isn't guaranteed. Carefully consider your treatment options and talk to your doctor about what clinical trials are open to you. Your participation in a clinical trial may help doctors better understand how to treat mesothelioma in the future.

Treatment for other types of mesothelioma
Pericardial mesothelioma and mesothelioma of the tunica vaginalis are very rare and can be very aggressive. Early-stage cancer may be removed through surgery. Doctors have yet to determine the best way to treat later stage cancers, though. Your doctor may recommend other treatments to improve your quality of life.

Reducing your exposure to asbestos may reduce your risk of mesothelioma. Most people with mesothelioma were exposed to the asbestos fibers at work. Workers who may encounter asbestos fibers include:

• Miners
• Factory workers
• Insulation manufacturers
• Railroad workers
• Ship builders
• Gas mask manufacturers
• Construction workers

Follow all safety precautions in your workplace, such as wearing protective equipment. You may also be required to shower and change out of your work clothes before taking a lunch break or going home. Talk to your doctor about other precautions you can take to protect yourself from asbestos exposure.

Older homes and buildings may contain asbestos. In many cases, it's more dangerous to remove the asbestos than it is to leave it intact. Breaking up asbestos may cause fibers to become airborne, where they can be taken into your body as you breathe. Consult experts trained to detect asbestos in your home. These experts may test the air in your home to determine whether the asbestos is a risk to your health. Don't attempt to remove asbestos from your home — hire a qualified expert.

Shock. Anger. Sadness. Despair. Confusion. You may be feeling one or all of these emotions after receiving a mesothelioma diagnosis. A cancer diagnosis is devastating not only to you, but to your family and loved ones. Take time to experience the sadness and despair and to grieve. As you're shuffled between appointments with various doctors and specialists, know that you can take control of the time you have remaining. You decide how you'll spend your time and whom you'll spend your time with. Along with your doctor, you determine which treatments you'll undergo.

In order to regain a sense of control, try to:

• Learn everything you can about mesothelioma. Write down a list of questions to ask your doctor. Ask your health care team for reading materials and other resources to help you better understand your disease. Consult the National Cancer Institute (NCI) and the American Cancer Society (ACS) for more information. Both organizations can provide you with information through their Web sites or toll-free telephone information lines. Call the NCI at 800-4-CANCER, or 800-422-6237. Call the ACS at 800-ACS-2345, or 800-227-2345. Information may help you feel more confident in your treatment decisions, and it may help you better understand what's going on inside your body.
• Surround yourself with a support network. Whether it's close friends or family or a combination of both, surround yourself with people who love you. These people can help you with the everyday tasks, such as getting you to appointments or treatment, and they can help support you by providing someone to talk to or to reassure you. If you have trouble asking for help, learn to be honest with yourself and accept help when you need it — your friends and family feel helpless too, and they want to help you.
• Seek out other people with cancer. Ask your health care team about cancer support groups in your community. Sometimes there are questions that can only be answered by other people with cancer. Support groups offer a chance to ask these questions and receive support from people who understand your situation. Online support message boards can offer similar benefits while allowing you to remain anonymous.
• Plan for the unknown. Ask your health care team about advance directives that give your family guidance on your medical wishes in case you can no longer speak for yourself. Talk to a lawyer about your will, if you haven't already done so.