Cancer is a condition that causes body cells to divide out of control and spread to different site. Practically it can occur anywhere in the billions of cells present in human body. Carcinogen is the substance that causes cancer. Epidemiological evidence suggests that quitting smoking, increasing fruit and vegetable eating, and controlling infections will all help to lower cancer rates. Other factors include avoiding excessive sun exposure, increasing physical activity, and reducing alcohol and perhaps red meat consumption. Modification of sex hormone levels is anticipated to be required for a significant reduction in breast cancer, and the development of viable technologies for doing so is a top research goal. The potential protective roles of certain antioxidants and other components of fruits and vegetables need to be clarified. Damage to the DNA of cancer cells causes the aberrant growth and division seen in this cell. Damage to and defects in cellular DNA can occur in a variety of ways. Environmental variables, such as cigarette smoke exposure, can set off a cascade of process that can leads DNA abnormalities, which further to cancer.it can occur through hereditary transmission. When cancer cells reproduce and proliferate, they frequently turn into tumour, which is a clump of cancer cells. Tumors pressurise, crush, and kill surrounding tissue, causing many of the symptoms of cancer. Normally human cells produce new cells by process of cell division according to body requirement. When cell get damaged and or became old they die and new cell are form and occupies their position. This multistep process can break down, causing aberrant to grow further reproduce.