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tumour
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A three-part illustration shows tumor development: first, cancer cells form a small tumor near the skin surface; second, the tumor grows as new blood vessels supply it with nutrients; third, the invasive tumor spreads into underlying tissues and blood vessels, with some cancer cells traveling to other parts of the body. Lung cancer Failure of DNA repair mechanismsDNA repair mechanisms maintain the integrity of DNA, which often acquires mutations during replication. If these mechanisms fail, or if the cell does not undergo apoptosis (a genetically encoded cell “suicide”), more mutations may occur, and the cells will proliferate. If the proliferation is slow and localized to the area in which it begins, the result is a benign tumour. With fast, uncontrolled growth and the invasion of other tissues, a malignant tumour arises.
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A three-part illustration shows tumor development: first, cancer cells form a small tumor near the skin surface; second, the tumor grows as new blood vessels supply it with nutrients; third, the invasive tumor spreads into underlying tissues and blood vessels, with some cancer cells traveling to other parts of the body.
As a tumour grows larger, it invades the healthy tissues nearby. Cancer spreads when cells from a tumour travel to other parts of the body.

tumour

pathology
Also known as: neoplasm, tumor
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Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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tumour, a mass of abnormal tissue that arises without obvious cause from preexisting body cells, has no purposeful function, and is characterized by a tendency to independent and unrestrained growth. Tumours are quite different from inflammatory or other swellings because the cells in tumours are abnormal in appearance and other characteristics. Abnormal cells—the kind that generally make up tumours—differ from normal cells in having undergone one or more of the following alterations: (1) hypertrophy, or...

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