Synonyms: Abnormal growth, Abnormal mass, Neoplasm

Medical Specialties: Oncology, Pathology

Clinical Definition

A tumor is any kind of swelling or enlargement of tissues involving abnormal growth anywhere in the body. A tumor can be cancerous or noncancerous (benign). However, benign tumors can still cause problems.

In Our Own Words

A tumor is an abnormal growth. Normally, cells in your body grow, divide and then die. In adults, cells normally divide in order to replace worn out or dying cells or to repair injuries. However, when the process goes wrong, new cells can form even if your body does not need them. Old cells may not die off in an orderly fashion. When this occurs, the extra cells can form an abnormal mass (tumor).

In most types of cancer, the cancer cells form a tumor; leukemia is an exception. When cancer cells travel to other parts of the body, they grow and form new tumors there, a process known as metastasis. 

Relevant Conditions
Common Types
  • Cancerous
  • Precancerous
  • Benign
Side Effects
Share this article
  • Harvard Medical School. "Medical Dictionary of Health Terms." Harvard Health Publications 2013.http://www.health.harvard.edu. Accessed Aug. 2013.
  • University of Maryland Medical Center. "Tumor." Medical Encyclopedia. May 2013. http://umm.edu. Accessed Aug. 2013.
  • American Cancer Society. "What is cancer?" Jan. 2013. http://www.cancer.org. Accessed Aug. 2013.
  • American Cancer Society. "Cancer guide." Jan. 2013. http://www.cancer.org. Accessed Aug. 2013.
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