proliferation

Cellular reproduction and programmed cell death (apoptosis) are normally closely regulated within populations of cells. Cell numbers increase when cellular reproduction outpaces cell death, and such cellular proliferation is normal under some circumstances, such as clonal expansion as part of the immune response.

However, tumors arise when cell proliferation escapes normal cellular controls. Benign tumors expand locally, but lack the other defining characteristic of malignancy, which is invasiveness both locally and at a distance (metastasis).

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