What is malignant mesothelioma?

What is malignant mesothelioma?
Malignant mesothelioma is a cancer that starts in cells in the linings of certain parts of the
body, especially the chest or abdomen.
A layer of specialized cells called mesothelial cells lines the inside of the chest, the
abdomen, and the space around your heart. These cells also cover the outer surface of
most of your internal organs. The lining formed by these cells is called mesothelium.
The mesothelium helps protect your organs by making a special lubricating fluid that
allows organs to move around. For example, this fluid makes it easier for the lungs to
move inside the chest during breathing. The mesothelium has different names in different
parts of the body:
• In the chest it is called the pleura .
• In the abdomen it is called the peritoneum.
• In the space around the heart it is called the pericardium.
Tumors of the mesothelium can be non-cancerous (benign) or cancerous (malignant).
Malignant mesothelioma
A cancerous tumor of the mesothelium is called a malignant mesothelioma, although this
is often shortened to just mesothelioma. Mesotheliomas can start in 4 main areas in the
• Pleural mesotheliomas start in the chest. They account for about 3 out of 4
• Peritoneal mesotheliomas begin in the abdomen. They make up most of the
remaining cases.  • Pericardial mesotheliomas start in the covering around the heart and are very rare.
• Mesotheliomas of the tunica vaginalis are very rare tumors that start in the covering
layer of the testicles.
Malignant mesotheliomas can also be classified into 3 main types based on how the cells
are arranged when looked at under a microscope:
• About 50% to 60% of mesotheliomas are epithelioid. This type tends to have a better
outlook (prognosis) than the other types.
• About 10% to 20% of mesotheliomas are sarcomatoid (fibrous).
• Mixed (biphasic) mesotheliomas have both epithelioid and sarcomatoid areas. They
make up about 30% to 40% of mesotheliomas.
Benign tumors of the mesothelium
Benign (non-cancerous) tumors can also start in the mesothelium. These tumors are
typically removed by surgery, and there is often no need for additional treatment.
Localized fibrous tumor of the pleura
This type of benign tumor can form in the pleura surrounding the lungs. It used to be
called benign fibrous mesothelioma, but doctors now know that this tumor actually starts
from tissue under the mesothelium and not from mesothelial cells. This disease is usually
benign, but about 1 in 10 are cancerous. A similar condition starting in the peritoneum is
called solitary fibrous tumor of the peritoneum.
Adenomatoid mesothelioma
This benign tumor can develop in the mesothelium of certain reproductive organs. In
men, it often starts in the epididymis (ducts that carry sperm cells out of the testicle). In
women, this tumor may begin in the fallopian tubes (tubes that carry eggs from the
ovaries to the uterus).
Benign cystic mesothelioma
This is a rare non-cancerous tumor that often begins in the peritoneum.

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