Malignant mesothelioma is a rare disorder and is often misdiagnosed. It is a disease that derives directly from the mesothelial cells in the serous membranes. But it is not uncommon for other growths to appear in the mesothelium, both cancerous and non cancerous.
Tumors of the mesothelium can be benign (non-cancerous) or cancerous. A malignant tumor of the mesothelium is called malignant mesothelioma, but because most mesothelial tumors are cancerous, the disease is often simply called mesothelioma.
Although uncommon, the mesothelium of certain female and male reproductive organs may develop a benign tumor called an adenomatoid tumor. In men, the tumor starts in the area where the sperm is carried from the testicles and in women it starts in the fallopian tubes. Another type of benign tumor that starts in the female reproductive organs is called a benign cystic mesothelioma.
A type of benign tumor that used to be called benign fibrous mesothelioma can form in the pleura around the lungs. It is now known that this type of tumor starts in the tissues under the mesothelium and therefore is not a type of mesothelioma. It is typically not cancerous, but can progress to cancer in some cases. A similar disease that forms in the peritoneum is called a fibrous tumor of the peritoneum. These types of tumors are often removed surgically, and no other treatment is needed.
The most common form of malignant tumors in the mesothelium are metastatic tumors. That is, the tumors start in another part of the body and then the cancer metastasizes and spreads to the mesothelium. The ratio is between 7: 1 to 20: 1 for the occurrence of these types of tumors versus a mesothelioma. Mesothelioma derives directly from the mesothelial cells and does not migrate into the mesothelium from other organs.
The most common metastatic tumors that grow in the pleura derive from, in descending order:
For the pericardial tumors from metastases, the most common originating organs are lung, breast and thyroid. In the peritoneum, the ovary, stomach, large intestine, pancreas and breast are the most common sources of metastatic tumors.
It is also known that leukemia and lymphoma can spread to the serous cavities without involving the pleura or peritoneum directly. One reason why mesothelioma is difficult to diagnose with X-rays and other imaging systems is that the presence of a cancerous growth in the mesothelium does not necessarily indicate that the patient has mesothelioma. Metastatic tumors appear the same on an X-ray.
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