What is Cancer?


Cancer is a disease that starts when cells in the body begin to grow and divide without control or order. These abnormal cells can form a mass of tissue called a tumor, which may invade adjoining tissues and organs. Cancer can also spread from one part of the body to other parts through the blood or lymph system. This process is called metastasis.

There are many different types of cancer. Each type begins in a specific part of the body and grows and spreads differently. Cancer can affect any part of the body, but it often begins in tissues that line other tissues and organs. These include the skin, lungs, liver, and stomach. Cancer can also start in tissues that make blood, such as bone marrow or the tissues that make and repair blood vessels. Other types of cancers develop in the bones or in connective tissue, such as muscles and cartilage.

Cancer develops when genes that control cell growth and division change. These genetic changes can be caused by normal events that happen during life or by exposure to carcinogens (cancer-causing agents).

Three types of genes are involved in causing cancer: proto-oncogenes, tumor suppressor genes, and DNA repair genes. When these genes are mutated, they allow cancer cells to grow and survive when they should not.

Most cancers develop because of multiple cellular mutations that accumulate over time. These mutations usually happen in tissues that are growing and dividing rapidly, such as cells that line the inside of the lungs or intestines or that create blood cells. Cancer cells can also develop when normal cells that make up a tissue, such as the skin or the tissue that lines the inside of an organ, become damaged and begin to grow and divide without control or order.

Many types of cancer can be prevented by avoiding tobacco and excessive alcohol use, eating a healthy diet, maintaining a healthy weight, exercising regularly, limiting exposure to sunlight and other forms of radiation, and practicing safer sex. Some cancers, such as esophageal and lung cancer, can be prevented by screening tests.

When a person has cancer, treatment may involve surgery to remove the tumor and other treatments, such as chemotherapy and radiation. Some of these treatments can destroy the cancerous cells and prevent them from spreading or coming back. Other treatments, such as hormone therapy and targeted drug treatment, block the abnormal behaviors that allow cancer cells to grow and spread. Still other treatments, such as cryoablation and immunotherapy, use the body’s own immune system to fight cancer cells. Finally, palliative care can help relieve health symptoms caused by the cancer.