Cancer is a group of many related diseases that begin in cells, the body’s basic building blocks. To understand cancer, it is helpful to know what happens when normal cells become cancerous. The body is made up of various types of cells. Healthy cells grow and divide to produce more cells as the body needs them. When this orderly process goes wrong, new cells form when the body does not need them and the old cells do not die when they should. The extra cells formed create a mass of tissue called a growth or a tumor; however, having a tumor does not indicate cancer. There are two types of tumors the body can form, benign and malignant.

Benign tumors are not cancerous and are rarely life threatening. Benign tumors can often be removed and in most cases do not come back. The cells in benign tumors do not spread to other parts of the body.

Malignant tumors are cancerous. The cells in malignant tumors are abnormal; they divide without control or order. These cancer cells invade and destroy healthy tissue around them. Cancer cells can break away from a malignant tumor and enter into the bloodstream or lymphatic system.

Scientists have discovered that cancer is caused by changes in genes that normally control the growth and death of cells. Certain lifestyle and environmental factors change normal genes to those that allow the growth of cancer. Many gene changes leading to cancer are the result of tobacco use, diet, exposure to ultraviolet (UV) radiation from the sun, or exposure to carcinogens (cancer-causing substances) in the workplace or in the environment. Some gene alterations are inherited from one or both parents. Having an inherited gene alteration does not guarantee a person will develop cancer, it only warns that the chance of developing cancer is increased. Scientists continue to examine factors that may increase or decrease the chance of developing cancer.
Becoming infected with viruses such as the human papillomavirus (HPV), Hepatitis B or C, and human immunodeficiency virus (HIV) increase the risk of some types of cancer. Cancer itself is not contagious. You cannot “catch” cancer from someone diagnosed with this disease. Scientists have also concluded that injuries such as bruises do not cause cancer.

1. American Cancer Society, Inc. Cancer Facts and Figures 2005. Atlanta: American Cancer Society, Inc., 2005. View PDF.