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.
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.
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.
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.
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.
