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A tumor (also known as a neoplasm) is an abnormal tissue growth. Neoplasm means "new formation." Tumors can be either malignant (cancerous) or nonmalignant (benign) but either type may require therapy to remove it or reduce its size. In either case the tumor's growth is unregulated by normal body control mechanisms. Usually the growth is not beneficial to the organ in which it is developing and may be harmful.

It is not known what triggers this abnormal growth. Normally cells are generated at a rate needed to replace those that die or are needed for an individual's growth and development. Muscle cells are added as one grows as are bone cells and others. Genetic controls modulate the formation of any given cells. The process of some cells becoming muscle cells, some becoming nerve cells, and so on is called cell differentiation. Tumor formation is an abnormality in cell differentiation.

A benign tumor is a well-defined growth with smooth boundaries. This type of tumor simply grows in diameter. A benign growth compresses adjacent tissues as it grows. A malignant tumor usually has irregular boundaries and invades the surrounding tissue. This cancer also sheds cells that travel through the bloodstream implanting themselves elsewhere in the body and starting new tumor growth. This process is called metastasis.

It is important that the physician determine which kind of tumor is present when one is discovered. In some cases this is not a simple matter. It is difficult to determine whether the growth is benign without taking a sample of it and studying the tissue under the microscope. This sampling is called a biopsy. Biopsy tissue can be frozen quickly, sliced thinly, and observed without staining (this is called a frozen section); or it can be sliced, stained with dyes, and observed under the microscope. Cancer tissue is distinctly different from benign.

A benign tumor can be lethal if it compresses the surrounding tissue against an immovable obstacle. A benign brain tumor compresses brain tissue against the skull or the bony floor of the cranium and results in paralysis, loss of hearing or sight, dizziness, and/or loss of control of the extremities. A tumor growing in the abdomen can compress the intestine and interfere with digestion. A comparison of benign and malignant tumor characteristics. Illustration by Hans & Cassidy. Courtesy of Gale Group. It also can prevent proper liver or pancreatic function. The benign tumor usually grows at a relatively slow pace and may stop growing for a time when it reaches a certain size.

A cancer may grow quite rapidly or slowly, but usually is irregular in shape. It invades the neighboring tissue instead of pressing it aside. Most importantly, a cancer sheds cells, that is, metastasizes, so that new cancer growths can spring up in areas distant from the original cancer. The cancerous cells also can establish a cancer in tissue that is different from the original cancer. A breast cancer could spread to bone tissue or to liver.

A benign tumor can be removed surgically if it is in a location that a surgeon can reach. A tumor growing in an unreachable area of the brain can be treated using radiation. It can also be treated by inserting thin probes through the brain tissue into the tumor and circulating liquid nitrogen through the probe to freeze the tumor. This operation is called cryosurgery.

A malignancy requires steps to remove it but consideration must be given to the possibility that the tumor has begun to metastasize. The main or primary tumor may be removed surgically but if the tumor has been growing for some time the patient also may require treatment with powerful drugs to kill any stray cells. This treatment is called chemotherapy. Chemotherapy allows the antitumor drug to be circulated throughout the body to counter any small tumor growths.



Carpi, J. "Progress Against Cancer." American Health 13 (October 1994): 15-16+.

DeVita, E. "Conquering Cancer." American Health 13 (November 1994): 66-73.

Xu, D., et al. "Downregulation of Telomerase Reverse Transcriptase mRNA Expression by Wild Type in Human Tumor Cells." Oncogene 19 (26 October 2000): 53.

Larry Blaser


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—The surgical removal of a small part of a tumor. The excised tissue is studied under the microscope to determine whether it is benign or malignant.


—Use of powerful drugs to kill cancer cells in the human body.


—The process by which cells take the form of a given type of tissue. That is, basic cells become muscle cells, neurons, stomach lining, kidney, or other cell types.


—Spreading of a cancerous growth by shedding cells that grow in other locales.

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