About 2,500-3,000 cases of malignant mesothelioma are diagnosed in the United States each year. This type of cancer, found in the lining of the chest (pleural) or abdomen (peritoneal), is rare, usually caused by exposure to airborne asbestos particles, and can remain without symptoms for up to 50 years after asbestos exposure.
A cancerous tumor of the mesothelium, the tissue that lines the lungs, stomach, heart and other organs, is called a malignant mesothelioma. In this disease, cancer cells are found in the pleura (the thin layer of tissue that lines the chest cavity and covers the lungs) or the peritoneum (the thin layer of tissue that lines the abdomen and covers most of the organs in the abdomen).
Types of Malignant Mesothelioma
- Pleural mesotheliomas start in the chest, and are the most common type of mesotheliomas.
- Peritoneal mesotheliomas start in the abdomen, and make up most of the remaining type.
- Pericardial mesotheliomas start in the covering around the heart and are very rare.
Malignant mesotheliomas can also be classified into four types based on how the cells are arranged when examined under a microscope:
- Epithelioid: Most common type. It tends to have the best prognosis.
- Sarcomatoid: Accounts for about 10-20 percent of mesotheliomas.
- Mixed: Contains both epithelioid and sarcomatoid cells. Accounts for about 30-40 percent of mesotheliomas.
- Desmoplastic: The rarest type.
Benign Tumors of the Mesothelium
It is important not to confuse malignant mesothelioma with benign (non-cancerous) tumors that begin in the mesothelium. These benign tumors are usually successfully removed by surgery, without requiring additional treatment, and include:
- Adenomatoid tumors develop in the mesothelium of certain reproductive organs, such as the epididymis (the duct that stores and carries sperm) in men, and the fallopian tubes (tubes that carry eggs from the ovaries to the uterus) in women.
- Benign cystic mesothelioma may begin in mesothelium near female reproductive organs.
- Solitary fibrous tumors of the pleura can form in the pleura surrounding the lungs. While usually benign, about 1 in 10 may become cancerous.
Malignant mesothelioma is characterized by a long dormant period – the amount of time it takes for signs and symptoms to appear – sometimes up to 40 or 50 years. As a result, it is often diagnosed at later, more difficult-to-treat, stages.
Most patients diagnosed with pleural mesothelioma report shortness of breath, pain under the rib cage and/or swelling or pain in the abdomen.
Symptoms of peritoneal mesothelioma, which starts in the abdomen, may include stomach pain, weight loss, nausea, and vomiting. In the event that there is a hernia present, fluid buildup may occur in the abdomen.