Normal cells transform into cancer cells because of damage to DNA, the material within a cell that provides each person’s genetic blueprint. Most DNA damage is caused by abnormalities that occur while a normal cell is reproducing or because of obvious environmental factors such as cigarette smoking or asbestos, a human carcinogen.
Breathing asbestos dust allows microscopic fibers to penetrate the lungs and damage the mesothelial cells, the layer of specialized cells that cover many internal organs including the lungs, abdomen and heart. Asbestos exposure causes various kinds of DNA damage and eventually leads to a signature cancer called malignant mesothelioma.
Malignant mesothelioma produces tumors that grow uncontrollably in the lining of the lung or abdomen. If the tumors first appear in the lining of the lung, the cancer is known as pleural mesothelioma. If a person swallows asbestos fibers, the mesothelioma may appear initially in the abdominal cavity. It is called peritoneal mesothelioma. On rare occasions, mesothelioma tumors may appear in the lining of the heart, a form of cancer called pericardial mesothelioma.
Mesothelioma is typically classified as one of three subtypes depending on the appearance of the cell structure under a microscope. The most common cell subtype is epitheliod. About 50 to 60 percent of people with mesothelioma have this type and patients with this type of mesothelioma have a better prognosis, according to the American Cancer Society.
About 10 to 20 percent of mesotheliomas are sarcomatoid and 30 to 40 percent contain a mix of epitheliod and scarmatoid cells.
Most cases of mesothelioma are linked to exposure to asbestos in a workplace, though the symptoms may not appear until decades after exposure when the worker is retired or near retirement. About three out of four people with mesothelioma are older than 65 years old. The risk of developing mesothelioma corresponds to how much asbestos a person was exposed to and how long the asbestos exposure lasted. The risk of developing mesothelioma is a lifetime risk for people exposed to asbestos.