Cancer is a hereditary disease. It is caused by certain mutations in the genes that control our cell functions, especially their ability to divide and grow. These mutations take place often and most of the time the human body is able to correct them on their own. It depends on the position where the mutation takes place which makes it harmful, beneficial or without any real difference. A single mutation in genes is unlikely to cause cancer and it takes various mutations in multiple genes that leads to cancer. This is why cancer is more common among older people who have had a lot of time to build up these mutations.