Mesothelioma
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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.
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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 peritoneum.
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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.
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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.
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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 asbestos-related diseases.
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.
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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.
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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 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.
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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.
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