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 peritoneum.
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 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.
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 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.
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 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.
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.
