Cancer is a group of diseases characterized by an uncontrolled growth of abnormal cells, and it is the result of an uncontrolled cell-cycle. If the spread of these abnormal cells is not controlled by radiation therapy or other means, then cancer can cause death. Most cancers take the form of tumors, although not all tumors are cancers. A tumor is simply a mass of new tissue that serves no physiological purpose. It can be benign, like a wart, or malignant, like cancer. Benign tumors are made up of cells similar to the surrounding normal cells and are enclosed in a membrane that prevents them from penetrating neighboring tissues. A malignant tumor, or cancer, is capable of invading surrounding structures, including blood vessels, the lymph system and nerves. These invading cells interfere with the normal functioning of different body cells, and it is because of this that death of the host tissue usually follows.
In addition to spreading to surrounding areas, cancer can also spread to distant sites by the blood and lymphatic circulation and so can produce invasive tumors in almost any part of the body. In 1997, approximately 1,500,000 people in the United States were diagnosed with cancer and approximately 600,000 died of the disease. Early screening for cancer is believed to be able to drastically reduce the number of deaths due to the disease. Knowing what to look for when detecting cancer, as well as knowing if you are in a high risk population are two aspects of early prevention which have been proven to increase survival rates and lower the length and severity of treatments.