Epithelioid: The most common (50-70 percent). Has the highest rate of survival of the three forms of malignant mesothelioma.
Sarcomatoid: 7-20 percent of diagnoses. More aggressive than, and has a lower rate of survival than, epithelioid mesothelioma.
Mixed/biphasic: 20-35 percent of diagnoses. Malignant tissue contains both epithelioid and sarcomatoid cells. Lower rate of survival than epithelioid.
There are also benign (noncancerous) tumors of the mesothelium, and these are also called mesothelioma.
Pleural: The most common (75 percent). Of the mesothelial tissue surrounding the lungs and lining the chest wall.
Peritoneal: Second-most common (10-20 percent). Of the mesothelial tissue surrounding the abdominal organs.
Pericardial: Of the mesothelial tissue surrounding the heart. Rare.
Mesothelioma of the tunica vaginalis testis (in men) or and tunica serosa uteri (in women): Of the mesothelial tissue surrounding the male or female internal reproductive organs. Rare.
Malignant mesothelioma is divided into three types of cancer cells: epitheliod, sarcomatoid and biphasic.
Epitheliod cancer cells have a tubular pattern with a distinct cell nucleus, and tend t be uniform in shape. The individual cells resemble cubes.
Sarcamatoid cancer cells typically are oval and irregular in shape, and have a less distinct nucleum that do epitheliod cells. This is the least common type of mesothelioma cancer cell.
Biphasic cancer cells consist of a combination of both epitheliod and sarcomatoid cells. In some instances of biphasic cancer cells, both epitheliod and sarcomatoid cells are intermixed throughout a tumor. In other cases, the epitheliod and sarcomatoid cells are clustered into type-specific groupings, often with transitional areas in between.
Side B: The biggest risk factor by far of developing mesothelioma is exposure to asbestos particles, often at work. Asbestos exposure occurred in 70-80 percent of people with mesothelioma. Diagnosis usually occurs 20 to 50 years after exposure, and even low levels of exposure can be carcinogenic to some. Family members of exposed people have higher rates of occurrence as well, due to particles brought into the home from work. Mesothelioma is more common in men, people over 65 and white people.
Other theorized risk factors include exposure to simian virus 40 through old polio vaccines, radioactive thorium dioxide and the asbestos-like mineral zeolite.
Mesothelioma is relatively rare. About 2,000 to 3,000 people are diagnosed in the U.S. each year, but these rates seem to be going down. The average life expectancy after diagnosis is one year. The 5-year relative mesothelioma survival rate is about 10 percent, but new treatments offered today may improve survival rates for those recently diagnosed.