Mesothelioma is an uncommon form of
cancer, usually associated with prolonged exposure to
asbestos, which affects the
pleura, a sac which surrounds the
lungs, the
peritoneum, the lining of the abdominal cavity, or the
pericardium, a sac that surrounds the
heart.
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, or have been
exposed to asbestos dust and fibre in other ways, such as by washing the
clothes of a family member who worked with asbestos, or by home
renovation using asbestos cement products.
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 exists in almost 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.
The combination of smoking and asbestos exposure significantly
increases a person's risk of developing cancer of the air passageways in
the lung. The Kent brand of cigarettes used asbestos in its filters for
the first few years of production in the 1950s and some cases of
mesothelioma have resulted. Smoking current cigarettes does not appear
to increase the risk of mesothelioma.
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.
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 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.
History (particular reference to Australia)
An article by Wagner, published in the
British Journal of Industrial Medicine in 1960, first established
mesothelioma as a disease arising from exposure to crocidolite asbestos.
The article ("Diffused Pleural Mesothelioma and Asbestos Exposure in the
North Western Cape Province") referred to over 30 case studies of people
who had suffered from mesothelioma in South Africa. Some exposures were
transient and some were mine workers.
In 1962 Dr McNulty reported the first diagnosed case of malignant
mesothelioma in an
Australian asbestos worker in the Medical Journal of Australia. The
worker had worked in the mill at the asbestos mine in
Wittenoom from 1948 to 1950.
In 1965 an article in the British Journal of Industrial Medicine
established that people who lived in the neighbourhoods of asbestos
factories and mines, but did not work in them, had contracted
mesothelioma.
Despite proof that the dust associated with asbestos mining and
milling causes asbestos related disease, mining began at Wittenoom in
1943 and continued until 1966. It is difficult to understand why the
mine and mill was allowed to initially open and operate without adequate
risk control measures; and why nothing was done to force the owner (CSR)
to clean them up, adopt safer work practices or close down their
operations.
In 1974 the first public warnings of the dangers of blue asbestos
were published in a cover story called "Is this Killer in Your Home?" in
Australia's Bulletin magazine. In 1978 the
Western Australian Government decided to phase out the town of
Wittenoom, following the publication of a Health Dept. booklet, "The
Health Hazard at Wittenoom", containing the results of air sampling and
an appraisal of worldwide medical information.
By 1979 the first writs for negligence related to Witternoom were
issued against CSR and its subsidiary ABA, and the Asbestos Diseases
Society was formed to represent the Wittenoom victims.
Source:
Worksafe, Western Australia (http://www.safetyline.wa.gov.au/institute/level2/course21/lecture95/l95_04.asp)
External links
Sources
The first version of this article was adapted from a public
domain U.S.
National Cancer Institute fact sheet at
http://cis.nci.nih.gov/fact/6_36.htm
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