Cancer develops when The cells in any part of the body start to grow out of control. There are many different kinds of cancer but all of them come back to this, abnormal cell growth. Throughout a persons life cells are constantly dividing and doubling to replace other dieing cells. Cancer cells continue to grow and divide without dieing. People develop cancer because of damaged DNA. Cancer is always traced back to DNA. Sometimes DNA can be damaged by something in the environment, such as smoking, in turn causing cancer. Most cancers cause tumors, with the exception of leukemia. Cancer cells often spread to other parts of the body through the bloodstream of lymph vessels, this is called metastasis. But also remember that not all tumors are cancerous. Different kinds of cancer are very different, and all cancers are treated in different ways. Cancer is the second leading cause of death in the united states. Half of all men and a third of all women will develop cancer at one point in there lives. The risks of getting cancer can be reduced by eating a good diet, exercising and not doing harmful things like smoking. Over 1 million people are diagnosed with cancer every year, 77% are in people over the age of 55, however young people do get cancer too. Rates of cancer differ in different ethnic groups. Today millions of people are living with cancer, The earlier it is detected the more treatable it is, and the longer a person can live with it. Many different cancers are caused by tobacco products, smoking cigarettes and cigars and chewing are cause for one third of all cancer deaths in the united states. Skin cancer, breast cancer, and prostate cancer come from other things, mostly age, skin cancer from spending too much time in the sun. There are many different factors but it is estimated the one third of cancers could be prevented with a better diet and more exercise. Most cancers can be avoided to a certain degree simply by avoiding tobacco products and alcohol.