The word cancer refers to a group of almost 200 different diseases that all start when some of the body's cells become abnormal, growing and multiplying very quickly. Normally, cells grow and divide to produce more cells only when the body needs them. But sometimes cells keep dividing when new cells are not needed. These extra cells may form a mass of tissue, called a growth or tumor. A tumor may be benign (non-cancerous) or malignant (cancerous).
Unlike normal cells, cancer cells multiply without any control. They don't self-destruct or die when they become worn out or damaged. Cancer cells crowd out healthy cells and prevent them from doing their jobs. They can also invade surrounding tissue or spread to distant areas of the body to create new tumors, a process called metastasis.
What causes cancer?
Cancer has no single cause. Usually we cannot know the exact cause of a cancer. The body contains millions of cells. Each cell contains DNA made up of thousands of genes that determine what the cell is supposed to do. Scientists have found that when certain genes are abnormal or become damaged, the cell may become cancerous.
Scientists have identified some factors that increase the risk of cancer, including chemicals in cigarette smoke and radiation from the sun. But there's no way to know exactly what factors were involved in starting anyone's cancer. We do know that cancer is not contagious (you can't catch it from someone else). There is currently no evidence that high levels of stress or anxiety cause cancer.
How is cancer diagnosed?
For most cancers, a biopsy is the only way to obtain an accurate diagnosis. Your doctor removes a sample of abnormal cells or tissue from the tumor. Then a pathologist (a doctor with special training in studying normal and diseased body tissues) views it under a microscope. Pathologists can determine if the tumor is cancer. If it is cancer, they identify the type of cancer and how quickly it is growing.
Most cancers are named for the organ or type of cell in which they begin, not necessarily the organ in which the tumor is found. For example, when a cancer starts in the breast and spreads to the brain and forms a tumor there, it is called breast cancer that has metastasized (spread) to the brain. It is not called brain cancer.
When cancer cells metastasize, lymph nodes are often one of the first areas to which they spread. Removing lymph nodes is a way to determine how likely it is that cancer cells have spread to other parts of the body.
Your doctor will use the information from the pathology report and from other tests to determine the stage of your cancer. The stage of the cancer tells how much cancer is in your body and where it is located.
For more information, visit Cancer Types and Topics.