Cell types:
Epithelioid: The most common (50-70 percent). Has the highest rate of survival of the three.
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.
Types:
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.
While the large majority of malignant mesotheliomas are pulmonary (i.e. of pleural origin), the tumor can also arise from cells of the peritoneum, pericardium, and tunica vaginalis of the testis. Mesothelial cells form the serosa which line the thoracic and abdominal cavities. They also contribute to the pericardium and the tunica vaginalis which surround the heart and testis, respectively. They are derived from embryonic mesoderm. Note that bronchiolar epithelium derives from endoderm, not mesoderm; and myocardial tissue, while mesodermal in origin, does not contain mesothelium. Most cases of malignant mesothelioma are associated with past history of asbestos exposure. Note that benign mesothelioma IS NOT associated with asbestos exposure.