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• Benign and malignant tumors
• Words to Know
• Medical approaches

A tumor is an abnormal growth of tissue. Also known as a neoplasm (meaning "new formation"), a tumor can be either benign (not serious or harmful) or malignant (cancerous or deadly). Either type may require therapy to remove it or reduce its size.

It is not known what triggers a tumor's abnormal growth. The body normally creates cells only at a rate needed to replace those that die or to aid an individual's growth and development. The growth of a tumor, however, is unregulated by normal body control mechanisms.

Benign and malignant tumors

A benign tumor is a well-defined growth with smooth boundaries that simply grows in diameter. This can be harmful if the tumor compresses the...