Mesothelioma typically develops 20 to 50 years after the initial exposure to asbestos. Most people get the initial exposure to asbestos in the young adulthood. Because of the long lag period between the exposure and development of mesothelioma, this disease generally develops in the older age group. Among persons who had been exposed to asbestos, the risk of development of mesothelioma varies depending on the intensity of exposure, and duration of exposure. The risk of mesothelioma also increases with passing time since the initial exposure; hence younger the age at the time of exposure, greater would be the risk of developing mesothelioma at adult age. The lag period between asbestos exposure and development of mesothelioma may vary with occupation. Insulators, and dockworkers have a shorter interval between asbestos exposure and mesothelioma compared to shipyard workers, maritime worker and domestic exposure. Median age of development of mesothelioma is about 60 years. Incidence of mesothelioma peaks in the age group 40 years to 70 years. Men outnumber women in mesothelioma development by a ration of 5 to 1. Three to four decades ago, the majority of the workforce in the industries related asbestos comprised o men and this would probably explain the high degree of disparity between the incidence of mesothelioma in males and females. There is no evidence to suggest that this difference in the incidence of mesothelioma is due to inherent genetic difference between males and females.
Majority of patients develop difficulty in breathing, chest wall pain or both of these symptoms and would present to a physician. These are the most common symptoms of mesothelioma. Physical examination by physician may show evidence of pleural effusion, or if the pleural effusion is minimal this may be demonstrated on a chest x-ray. 95% of patients will develop pleural effusion sometime during the course of their disease. Chest x-ray may also demonstrate the presence of mass on the chest wall or outer aspect of the lung. In some patients these abnormalities may be subtle and may not produce any symptoms. Mesothelioma may be an incidental finding picked up on chest x-ray or CT scan done for some other purposes. In some patients the tumor may cause air to leak from the lung to the pleural cavity (condition known as pneumothorax) and may lead to difficulty in breathing. Right side of the chest is more commonly involved with penumthorax in mesothelioma patients than the left side. Right side of the pleural cavity is more commonly affected adverse events related to mesothelioma. Some patients may initially have bilateral pleural effusion and significant shortness of breath.