Mesothelioma is a very rare form of cancer. Approximately 3000 people are diagnosed each year with mesothelioma in the United States. Mesothelioma is only caused by exposure to asbestos, however, most people over the age of 40 have been exposed to asbestos at some point in their lifetime. One would believe that because most people over the age of 40 have been exposed to asbestos at some point in their lifetime, that the number of people diagnosed with mesothelioma would be much higher. However, there is an important medical principle called Individual Susceptibility. Essentially, it means not everyone will have the same reaction to a toxic agent. In other words, not everyone exposed to asbestos gets cancer. This means that there is differences in how each person responds when exposed to a toxic substance. In the case of mesothelioma cancer the toxic substance is asbestos. This explains why, for example, only one Navy veteran out of many who worked in the boiler room on a navy ship later developed mesothelioma while their colleagues remained virtually unaffected by the asbestos exposure. Therefore, if you fear that you have worked with or have been exposed to asbestos at some point during your lifetime, it is unlikely that you will develop mesothelioma cancer.