Mesothelioma: Medical
Questions and Answers
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 particles.
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.