Cancer starts when cells change (mutate) and grow out of control. The changed (abnormal) cells often grow to form a lump or mass called a tumor. Cancer cells can also grow into (invade) nearby areas. And they can spread to other parts of the body. This is called metastasis.

The mesothelium is thin tissue that covers and protects the outer surface of some organs. These include the lungs, stomach, and heart. It also lines body cavities, like the chest and belly (abdomen). It makes fluid that helps the organs slide against each other when you move and breathe.

Malignant mesothelioma is a rare kind of cancer that starts in the mesothelium. It's often called just mesothelioma. It most often starts in the mesothelium that surrounds the lungs (pleura). This cancer is called pleural mesothelioma.

The mesothelium that lines the abdomen is called the peritoneum. If the cancer starts there, it's called peritoneal mesothelioma.

Very rarely, mesothelioma can start in the lining around the heart (pericardium) or the lining covering the testicles (tunica vaginalis).

Unlike many other types of cancer, mesothelioma often doesn't grow as a tumor. Instead it grows along the thin tissue. Over time, mesothelioma can grow into nearby tissues and organs and spread to other parts of the body.

A risk factor is anything that may increase your chance of having a disease. The exact cause of someone's cancer may not be known. But risk factors can make it more likely for a person to have cancer. Some risk factors may not be in your control. But others may be things you can change.

The risk factors for mesothelioma include:

• Exposure to asbestos
• Cancer treatment with high doses of radiation to the chest or belly (abdomen)
• Being age 65 or older
• Being a man
• Exposure to minerals called zeolites
• An inherited BAP1 gene mutation

Talk with your doctor about your risk factors for mesothelioma and what you can do about them.

There's no sure way to prevent mesothelioma. But it's important to stay away from or limit exposure to asbestos. This is a big concern for people who work in certain industries. These include construction, insulation manufacturing, and textile manufacturing. Follow all safety precautions. You may need to wear protective clothing and a respirator.

Many older homes and other buildings may be made with materials that contain asbestos. If you think asbestos may be in your home, ask an expert to check your home. Don't disturb asbestos or try to remove it yourself. If needed, hire a trained asbestos expert to check and remove asbestos in your home.

There are no screening tests for mesothelioma in people at average risk. Screening tests are done to check for disease in people who don't have symptoms.

If you've been exposed to large amounts of asbestos, talk with your doctor. Some doctors may suggest tests to look for early signs of this cancer. These include CT scans or X-rays.

Mesothelioma often doesn't cause symptoms until it's been there for a long time. Symptoms depend on where the cancer is.

Pleural mesothelioma (in the chest) can cause symptoms, such as:

• Breathing problems, such as shortness of breath
• Cough
• Chest or low back pain
• Trouble swallowing
• Face or arm swelling
• Feeling tired
• Hoarseness

Peritoneal mesothelioma (in the abdomen) can cause symptoms, such as:

• Pain in your belly
• Swelling or fluid in your belly
• Nausea or vomiting
• Constipation

General symptoms of mesothelioma anywhere in the body include:

• Fever
• Extreme tiredness (fatigue)
• Losing weight without trying
• No desire to eat
• Sweating a lot and night sweats
• Blood-clotting problems

Many of these may be caused by other health problems. Still, it's important to see a doctor if you have these symptoms. Only a doctor can tell if you have cancer.

Mesothelioma is most often diagnosed when you see your doctor because of symptoms you are having. The doctor will ask you about your health history, symptoms, risk factors, and family history of disease. A physical exam will be done.

You may also have one or more of these tests:

• X-rays
• CT scan
• Biopsy
• Blood tests

After a diagnosis of mesothelioma, you'll need more tests. These help your doctors learn more about your cancer. They can help find out the stage of the cancer. The stage is how big it is and how far it has spread (metastasized) in your body. It's one of the most important things to know when deciding how to treat the cancer.

Once your cancer is staged, your doctor will talk with you about what the stage means for your treatment. Ask them to explain the details of your cancer to you in a way you can understand.

Your treatment choices depend on the type of mesothelioma you have, how big it is, if it has spread, test results, and the stage of the cancer. The goal of treatment may be to control the cancer or to ease problems it's causing. Talk with your health care team about your treatment choices, the goals of treatment, and what the risks and side effects may be.

Types of treatment for cancer are either local or systemic. Local treatments remove, destroy, or control cancer cells in one area. Surgery and radiation are local treatments. Systemic treatment is used to destroy or control cancer cells that may have traveled around your body. When taken by pill or injection, chemotherapy and targeted therapy are systemic treatments. You may have just one treatment or a combination of treatments.

Mesothelioma may be treated with:

• Surgery
• Radiation
• Chemotherapy (chemo)
• Targeted therapy
• Immunotherapy

Talk with your doctors about your treatment choices. Make a list of questions. Think about the benefits and possible side effects of each choice. Talk about your concerns with your doctor before making a decision.

Cancer treatments, such as chemotherapy and radiation, can damage normal cells. This can cause side effects, such as hair loss, mouth sores, and vomiting.

Talk with your doctor about side effects you might have and ways to manage them. There may be things you can do and medicines you can take to help prevent or control side effects.

Many people feel worried, depressed, and stressed when dealing with cancer. Getting treatment for cancer can be hard on your mind and body. Keep talking with your health care team about problems or concerns you have. Work together to ease the effect of cancer and its symptoms on your daily life.

Here are tips:

• Talk with your family or friends.
• Ask your health care team or social worker for help.
• Speak with a counselor.
• Talk with a spiritual advisor, such as a minister or rabbi.
• Ask your health care team about medicines for depression or anxiety.
• Keep socially active.
• Join a cancer support group in person or online.

Cancer treatment is also hard on the body. To help yourself stay healthier, try to:

• Eat a healthy diet, with a focus on high-protein foods.
• Drink plenty of water, fruit juices, and other liquids.
• Keep physically active.
• Rest as much as needed.
• Talk with your health care team about ways to manage treatment side effects.
• Take your medicines as directed by your team.

Your doctor will talk with you about when to call. You may be told to call if any of the following occur:

• New symptoms or symptoms that get worse
• Signs of an infection, such as a fever
• Side effects of treatment that affect your daily function or don't get better with treatment

Ask your doctor what signs to watch for, and when to call. Know how to get help after office hours and on weekends and holidays.

• Malignant mesothelioma is a rare kind of cancer that starts in the mesothelium. This is the thin tissue that covers and protects the outer surface of some organs, including the lungs, stomach, and heart.
• Unlike many other types of cancer, mesothelioma often doesn't grow as a tumor. Instead it grows along the thin tissue.
• Over time, mesothelioma can grow into nearby tissues and organs and spread to other parts of the body.
• There's no sure way to prevent mesothelioma. But it's important to stay away from or limit exposure to asbestos.
• Treatment choices include surgery, chemotherapy, radiation therapy, immunotherapy, and targeted therapy.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions, especially after office hours or on weekends and holidays.