A tumor (TOO-mor) is an abnormal growth of new tissue that can occur in any of the body's organs. Many people automatically associate tumors with the disease called cancer * , but cancer is not always present when someone has a tumor.

What Is a Tumor?

The human body is made up of many types of cells that are constantly dividing to produce new, younger cells that can “take over” for aging or damaged cells. Through this process, the body heals its injuries and keeps tissues healthy. Sometimes, this process gets out of control, and new cells continue to be produced even when they are not needed, forming a clump of extra tissue, a tumor.

There are two types of tumors:

A comparison of the characteristics of a benign tumor (top) and a malignant tumor (bottom).

A comparison of the characteristics of a benign tumor (top) and a malignant tumor (bottom).
Illustration by Hans of Cassady, Inc. © 2016 Cengage Learning®.

Who Gets Tumors?

People of all ages can develop tumors, but generally they are more common as people grow older. Researchers believe that malignant tumors result from a combination of causes, the most important being genetic and environmental. People may inherit a tendency to develop certain kinds of tumors from their parents. Also, repeated exposure to harmful substances such as cigarette smoke, pollutants, and too much sunlight can damage cells and trigger the process of tumor formation.

When a tumor first starts to develop, it is so small that it does not cause symptoms. As it grows, it usually causes symptoms that vary according to its location. For instance, a tumor in the lung may cause a feeling of irritation or a nagging cough. People with brain tumors may experience headaches, dizziness, blurry vision, or loss of coordination. A person with a tumor in the colon * may notice that going to the bathroom is painful or produces blood.

How Are Tumors Diagnosed and Treated?

A doctor can usually diagnose a tumor with one of many tests that create images of the inside of the body, such as x-rays, ultrasound * , CT scans * , or MRIs * . The next step is to figure out whether the tumor is benign or malignant through a process called biopsy (BY-op-see). Surgeons remove part or all of the tumor and examine a sample under a microscope. The appearance of the cells indicates whether a tumor is cancerous.

Even though a benign tumor is not harmful, it may have to be removed if it causes pain, pressure, or other symptoms. In many cases of malignancy, the tumor and any affected surrounding tissue will be removed. Sometimes, radiation therapy (directed high-energy x-rays) or chemotherapy (cancer-fighting drugs) may be used to shrink the tumor.

See also Brain Tumor • Cancer: Overview • Tobacco-Related Diseases: Overview


Books and Articles

Todd, Robert F., Kathleen A. Cooney, Teresa G. Hayes, Martha Pritchett Mims, and Francis P. Worden. Tumor Board Review: Guideline and Case Reviews in Oncology, 2nd ed. New York: Demos Medical, 2015.


MedlinePlus. “Tumor.” U.S. National Library of Medicine. https://www.nlm.nih.gov/medlineplus/ency/article/001310.htm (accessed November 18, 2015).

NHS Choices. “Benign Brain Tumour (Non-cancerous).” National Health Service. (accessed November 18, 2015).


American Brain Tumor Association. 8550 W. Bryn Mawr Ave., Ste. 550, Chicago, IL 60631. Telephone: 773-577-8750. Website: http://www.abta.org (accessed November 18, 2015).

American Cancer Society. 250 Williams St. NW, Atlanta, GA 30303. Toll-free: 800-227-2345. Website: http://www.cancer.org (accessed November 18, 2015).

National Cancer Institute. 9609 Medical Center Dr., Bldg. 9609, MSC 9760, Bethesda, MD 20892-9760. Toll-free: 800-4-CANCER. Website: http://www.cancer.gov (accessed November 18, 2015).

* cancer is a condition characterized by abnormal overgrowth of certain cells, which may be fatal.

* colon (KO-lin), also called the large intestine, is a muscular tube through which food passes as it is digested, just before it moves into the rectum and out of the body through the anus.

* ultrasound, also called a sonogram, is a diagnostic test in which sound waves passing through the body create images on a computer screen.

* CT scans is the shortened name for computed tomography (to-MOG-ra-fee), which uses computers to view structures inside the body. Formerly called computerized axial tomography (CAT).

* MRI, which is short for magnetic resonance imaging, produces computerized images of internal body tissues based on the magnetic properties of atoms within the body.

  This information is not a tool for self-diagnosis or a substitute for professional care.