Mesothelioma is a rare type of cancer that primarily affects the lining of the lungs, but can also affect the heart, abdomen and other organs. Approximately 2,000 to 3,000 cases of mesothelioma cancer are diagnosed each year in the United States, comprising around .3 percent of all cancer diagnoses. The average age at diagnosis is 62 years of age, occurs about four times more frequently in men than in women and is almost always caused by exposure to asbestos. The life expectancy for mesothelioma patients is generally reported as less than one year following diagnosis, however, a patient's prognosis can be positively affected by numerous factors including how early the cancer is diagnosed and how aggressively it is treated.