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Mesothelioma is a rare form of cancer in which malignant
(cancerous) cells are found in the mesothelium, a protective sac that
covers most of the body's internal organs. Most people who develop
mesothelioma have worked on jobs where they inhaled asbestos
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 or
Incidence of 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
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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. It caused an industrial revolution prior to the 70s
but was quickly dismissed when research discovered its link to cancer.
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.
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 exposure.
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
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.
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.
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
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.
Diagnosis of mesothelioma
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
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.
Staging of mesothelioma
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 treatment.
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.
Treatment of mesothelioma
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 combined.
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.
Because mesothelioma is very hard to control, the U.S. 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.