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.
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.
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? Over 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. See statistics for more details.
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 the majority of cases.
However, mesothelioma has been reported in some individuals without
any known exposure to asbestos. Click here to learn more about asbestos
Who is at increased risk for developing mesothelioma? Since
the early 1940s, millions of American workers have been exposed to
asbestos dust. An increased risk of developing mesothelioma was originally
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 trades people. 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.
There is 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.
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.
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 biopsy confirms a diagnosis of mesothelioma. In a biopsy, a surgeon
or a medical oncologist removes a sample of tissue for examination
under a microscope by a pathologist. (See Pathology Diagnosis to learn
why some patients request a second opinion.)
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.
What is the conventional approach to treating mesothelioma? 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. Standard treatment for all but localized
mesothelioma is generally not curative. 1 (See
survival rates for median survival rates
with different treatments.)
Surgery - Extrapleural pneumonectomy in selected patients
with early stage disease may improve recurrence-free survival, but
its impact on overall survival is unknown. Pleurectomy and decortication
can provide palliative relief from symptomatic effusions, discomfort
caused by tumor burden, and pain caused by invasive tumor.
Operative mortality from pleurectomy/decortication is <2%, while mortality
from extrapleural pneumonectomy has ranged from 6% to 30%. 2
Radiation/Chemotherapy - The use of radiation therapy in
pleural mesothelioma has been shown to alleviate pain in the majority
of patients treated; however, the duration of symptom control is short-lived.
Single-agent and combination chemotherapy have been evaluated in single
and combined modality studies. The most studied agent is doxorubicin,
which has produced partial responses in approximately 15% to 20% of
patients studied. Some combination chemotherapy regimens have been
reported to have higher response rates in small phase II trials; however,
the toxic effects reported are also higher, and there is no evidence
that combination regimens result in longer survival or longer control
of symptoms. 3
Alimta - The only FDA approved chemotherapy for malignant
pleural mesothelioma (in combination with cisplatin) is pemetrexed
(Alimta). In the key clinical trial that led to its approval, Alimta
was combined with another chemotherapy drug (cisplatin) and compared
with cisplatin alone. The patients who received the two drugs (Alimta
and cisplatin) had their cancers progress (grow/spread) in 5.7 months
(median). The patients who only received cisplatin had their tumors
progress in 3.9 months (median). The median survival for the patients
who received both drugs was 12.1 months versus 9.3 months for cisplatin
only. 4
For some physicians, these therapeutic gains are not impressive. For
example, some have written, "For the treatment of mesothelioma, there
is little evidence that current therapies (chemotherapy, radiation,
surgery) provide significant benefit for survival or quality of life.[R]adical
treatments, occupying the 3 months after diagnosis, can take up the
best 3 months that the patient might have had.Malignant mesothelioma
has largely defeated treatment...
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