Name the three forms of MESOTHELIOMAS, their frequency, and their distinguishing characteristics.
Regardless of the location, malignant mesotheliomas occur in three forms. The epithelioid type is the most common, accounting for 50-70% of all mesotheliomas. Between 20-35% of mesotheliomas are sarcomatoid, or fibrous. These cells are typically oval shaped, but more irregular, and with the nucleus not as clearly visible under an electron microscope as the nuclei of the epithelioid mesothelioma cancer cells. Because the oval irregular shape is a common form of a cancer cell type, sarcomatoid mesothelioma can be confused with sarcomatoid carcinoma and with sarcoma. The remaining 7-20% of tumors are classified as mixed/biphasic. Epithelioid mesothelioma has the best outlook for survival. Biphasic mesothelioma cancer typically produces a combination of epithelioid and sarcomatoid cancer cells as opposed to a mixture, meaning that the two subtypes occur in different parts of the tumor.