Definition
Mesothelioma is an unusual disease that causes malignant
cancer cells to form within the lining of the chest, abdomen, or around the
heart. Its primary cause is believed to be exposure to asbestos.
Description
Malignant
mesothelioma is also known as asbestos cancer or simply "meso."
Mesothelioma causes cancerous cells to develop in the body's mesothelium, where
they can spread to and damage vital organs and tissue. These malignant cells
can also metastasize to other regions of the body. Mesothelioma is very
difficult to diagnose and responds poorly to most treatment modalities,
accounting for a poor prognosis.
The
disease derives its name from the mesothelium, a sac-like membrane that
protects most of the body's internal organs. It is divided into two distinct
protective layers of cells: the visceral (the layer directly surrounding the
organ) and the parietal (a sac around the body cavity). By releasing a
lubricating fluid, the mesothelium allows the organs to move more freely within
the body cavity; for example, the contraction and expansion of the lungs. The
mesothelium is also referred to according to where it is located in the body: pleura
(chest), peritoneum (abdomen), and pericardium (heart).
Over
two-thirds of all mesothelioma cases begin in the pleura region. Pleural
mesothelioma spreads through the chest cavity, occasionally developing in the
lungs as well. The disease most commonly causes pleural effusion, an excess build-up of fluid inside the chest
cavity. This excess fluid increases pressure on the lungs and restricts
breathing. In addition, malignant cells can cause the pleural lining to thicken
and restrict the breathing space even further.
Peritoneal mesothelioma is the second most common form of
the disease, accounting for less than 30% of all cases. Malignant cells form in
the peritoneum, affecting the abdomen, bowel, liver, and spleen. Similar to
pleural mesothelioma, the disease also causes a build up of excess fluid in the
abdominal cavity. Normal bodily functions, such as digestion, can be hindered
by the obstruction of organ movement.
Very
rare forms of mesothelioma occur in the pericardium, as well as the mesothelium
of the male and female reproductive organs. Cystic mesothelioma of the
peritoneum, another rare form of the disease, occurs predominantly in women and
is more benign in nature.
Malignant mesothelioma takes the form of one of three
cell-types: epithelioid (50% to 70% of cases), sarcomatous (7% to 20% of
cases), and biphasic/mixed (20% to 35% of cases). Of these cell-types,
epithelioid mesothelioma carries the most favorable prognosis, followed by
biphasic, and finally sarcomatous (very aggressive).
Mesothelioma
remains relatively uncommon in the United States, with approximately 2,500 new
cases reported annually. The incidence rates are much higher in Western Europe
(over 5,000 cases reported annually). These numbers are expended to climb
dramatically over the next 20 years. Older males (median age 60 at diagnosis)
are three to five times more likely to develop mesothelioma than women. This is
most like do to male predominance in those professions with an increased risk
of asbestos exposure
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