cancer, in medicine, common term for neoplasms, or tumors, that are malignant. Like benign tumors, malignant tumors do not respond to body mechanisms that limit cell growth. Unlike benign tumors, malignant tumors consist of undifferentiated, or unspecialized, cells that show an atypical cell structure and do not function like the normal cells from the organ from which they derive. Cancer cells, unlike normal cells, lack contact inhibition; cancer cells growing in laboratory tissue culture do not stop growing when they touch each other on a glass or other solid surface but grow in masses several layers deep.
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