- What is the mesothelium?
The mesothelium is a membrane that covers and protects most of the internal
organs of the body. It is composed of two layers of cells: One
layer immediately surrounds the organ; the other forms a sac
around it. The mesothelium produces a lubricating fluid that is
released between these layers, allowing moving organs (such as the
beating heart and the expanding and contracting lungs) to glide easily against adjacent structures.
The mesothelium has different names, depending on its location
in the body. The peritoneum is the mesothelial tissue that covers most of the organs in the abdominal cavity. The pleura is the membrane that surrounds the lungs and
lines the wall of the chest cavity. The pericardium covers and
protects the heart. The mesothelial tissue surrounding the male
internal reproductive organs is called the tunica vaginalis
testis. The tunica serosa uteri covers the internal reproductive
organs in women.
- What is mesothelioma?
Mesothelioma (cancer of the mesothelium) is a disease in which
cells of the mesothelium become abnormal and divide without control or order. They can
invade and damage nearby tissues and organs. Cancer cells can also
metastasize (spread) from their original site to other
parts of the body. Most cases of mesothelioma begin in the pleura
- How common is mesothelioma?
Although reported incidence rates have increased in the past 20 years,
mesothelioma is still a relatively rare cancer. About 2,000 new
cases of mesothelioma are diagnosed in the United States each
year. Mesothelioma occurs more often in men than in women and risk
increases with age, but this disease can appear in either men or
women at any age.
- What are the risk factors for mesothelioma?
Working with asbestos is the major risk factor for
mesothelioma. A history of asbestos exposure at work is reported
in about 70 percent to 80 percent of all cases. However,
mesothelioma has been reported in some individuals without any
known exposure to asbestos.
Asbestos is the name of a group of minerals that occur naturally as masses of strong,
flexible fibers that can be separated into thin threads and woven.
Asbestos has been widely used in many industrial products,
including cement, brake linings, roof shingles, flooring products,
textiles, and insulation. If tiny asbestos particles float in the
air, especially during the manufacturing process, they may be
inhaled or swallowed, and can cause serious health problems. In
addition to mesothelioma, exposure to asbestos increases the risk
of lung cancer, asbestosis (a noncancerous, chronic lung ailment), and other cancers, such as those
of the larynx and kidney.
Smoking does not appear to increase the risk of mesothelioma.
However, the combination of smoking and asbestos exposure
significantly increases a person’s risk of developing cancer of
the air passageways in the lung.
- Who is at increased risk for developing mesothelioma?
Asbestos has been mined and used commercially since the late
1800s. Its use greatly increased during World War II. Since the
early 1940s, millions of American workers have been exposed to
asbestos dust. Initially, the risks associated with asbestos
exposure were not known. However, an increased risk of developing
mesothelioma was later found among shipyard workers, people who
work in asbestos mines and mills, producers of asbestos products,
workers in the heating and construction industries, and other
tradespeople. Today, the U.S. Occupational Safety and Health
Administration (OSHA) sets limits for acceptable levels of
asbestos exposure in the workplace. People who work with asbestos
wear personal protective equipment to lower their risk of
The risk of asbestos-related disease increases with heavier
exposure to asbestos and longer exposure time. However, some
individuals with only brief exposures have developed mesothelioma.
On the other hand, not all workers who are heavily exposed develop
There is some evidence that family members and others living
with asbestos workers have an increased risk of developing
mesothelioma, and possibly other asbestos-related diseases. This
risk may be the result of exposure to asbestos dust brought home
on the clothing and hair of asbestos workers. To reduce the chance
of exposing family members to asbestos fibers, asbestos workers
are usually required to shower and change their clothing before
leaving the workplace.
- What are the symptoms of mesothelioma?
Symptoms of mesothelioma may not appear until 30 to 50 years
after exposure to asbestos. Shortness of breath and pain in the
chest due to an accumulation of fluid in the pleura are often
symptoms of pleural mesothelioma. Symptoms of peritoneal mesothelioma include weight loss and
abdominal pain and swelling due to a buildup of fluid in the abdomen. Other symptoms of peritoneal mesothelioma may
include bowel obstruction, blood clotting abnormalities, anemia, and fever. If the cancer has spread beyond the
mesothelium to other parts of the body, symptoms may include pain,
trouble swallowing, or swelling of the neck or face.
These symptoms may be caused by mesothelioma or by other, less
serious conditions. It is important to see a doctor about any of
these symptoms. Only a doctor can make a diagnosis.
- How is mesothelioma diagnosed?
Diagnosing mesothelioma is often difficult, because the
symptoms are similar to those of a number of other conditions.
Diagnosis begins with a review of the patient’s medical history,
including any history of asbestos exposure. A complete physical examination may be performed, including x-rays of the chest or abdomen and lung function tests.
A CT (or CAT) scan or an MRI may also be useful. A CT scan is a series of detailed pictures of areas inside
the body created by a computer linked to an x-ray machine. In an
MRI, a powerful magnet linked to a computer is used to make
detailed pictures of areas inside the body. These pictures are
viewed on a monitor and can also be printed.
A biopsy is needed to confirm a diagnosis of mesothelioma.
In a biopsy, a surgeon or a medical oncologist (a doctor who specializes in diagnosing and
treating cancer) removes a sample of tissue for examination under
a microscope by a pathologist. A biopsy may be done in different ways,
depending on where the abnormal area is located. If the cancer is
in the chest, the doctor may perform a thoracoscopy. In this
procedure, the doctor makes a small cut through the chest wall and puts a thin, lighted tube called a
thoracoscope into the chest between two ribs. Thoracoscopy allows
the doctor to look inside the chest and obtain tissue samples. If
the cancer is in the abdomen, the doctor may perform a
peritoneoscopy. To obtain tissue for examination, the doctor makes
a small opening in the abdomen and inserts a special instrument
called a peritoneoscope into the abdominal cavity. If these
procedures do not yield enough tissue, more extensive diagnostic
surgery may be necessary.
If the diagnosis is mesothelioma, the doctor will want to learn
the stage (or extent) of the disease. Staging involves more tests in a careful attempt to find
out whether the cancer has spread and, if so, to which parts of
the body. Knowing the stage of the disease helps the doctor plan
Mesothelioma is described as localized if the cancer is found only on the membrane
surface where it originated. It is classified as advanced if it
has spread beyond the original membrane surface to other parts of
the body, such as the lymph nodes, lungs, chest wall, or abdominal organs.
- How is mesothelioma treated?
Treatment for mesothelioma depends on the location of the
cancer, the stage of the disease, and the patient’s age and
general health. Standard treatment options include surgery, radiation therapy, and chemotherapy. Sometimes, these treatments are
- Surgery is a common treatment for
mesothelioma. The doctor may remove part of the lining of the
chest or abdomen and some of the tissue around it. For cancer of
the pleura (pleural mesothelioma), a lung may be removed in an
operation called a pneumonectomy. Sometimes part of the diaphragm, the muscle below the lungs that helps with
breathing, is also removed.
- Radiation therapy, also called radiotherapy, involves the use of high-energy rays to
kill cancer cells and shrink tumors. Radiation therapy affects the cancer cells
only in the treated area. The radiation may come from a machine
(external radiation) or from putting materials that
produce radiation through thin plastic tubes into the area where
the cancer cells are found (internal radiation therapy).
- Chemotherapy is the use of anticancer drugs
to kill cancer cells throughout the body. Most drugs used to
treat mesothelioma are given by injection into a vein (intravenous, or IV). Doctors are also studying the effectiveness of
putting chemotherapy directly into the chest or abdomen (intracavitary chemotherapy).
To relieve symptoms and control pain, the doctor may use a
needle or a thin tube to drain fluid that has built up in the
chest or abdomen. The procedure for removing fluid from the chest
is called thoracentesis. Removal of fluid from the abdomen is
called paracentesis. Drugs may be given through a tube in the
chest to prevent more fluid from accumulating. Radiation therapy
and surgery may also be helpful in relieving symptoms.
- Are new treatments for mesothelioma being studied?
Yes. Because mesothelioma is very hard to control, the National Cancer Institute (NCI) is sponsoring clinical trials (research studies with people) that are
designed to find new treatments and better ways to use current
treatments. Before any new treatment can be recommended for
general use, doctors conduct clinical trials to find out whether the treatment is
safe for patients and effective against the disease. Participation
in clinical trials is an important treatment option for many
patients with mesothelioma.
People interested in taking part in a clinical trial should
talk with their doctor. Information about clinical trials is
available from the Cancer Information Service (CIS) (see below) at 1–800–4–CANCER. Information
specialists at the CIS use PDQ®, NCI’s cancer information
database, to identify and provide detailed information about
specific ongoing clinical trials. Patients also have the option of
searching for clinical trials on their own. The clinical trials
page on the NCI’s Cancer.gov Web site, located at http://www.cancer.gov/clinical_trials
on the Internet, provides general information about clinical
trials and links to PDQ.
People considering clinical trials may be interested in the NCI
booklet Taking Part in Clinical Trials: What Cancer Patients
Need To Know. This booklet describes how research studies are
carried out and explains their possible benefits and risks. The
booklet is available by calling the CIS, or from the NCI
Publications Locator Web site at http://www.cancer.gov/publications
on the Internet.