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A tumor suppressor gene is a gene that reduces the probability that a cell in a multicellular organism will turn into a tumor cell. A mutation or deletion[?] of such a gene will increase the probability of a tumor. In that way, a tumor suppressor gene is similar to an oncogene.

Tumor suppressor genes, or more precisely, the proteins they code for, have a dampening or repressive effect on the regulation of the cell cycle. This is basically done by the tumor suppression genes/proteins in three ways :

1. Repression of genes[?] that are essential for the continuing of the cell cycle. If these genes are not expressed, the cell cycle will not continue, effectively inhibiting cell division.
2. Coupling the cell cycle to DNA damage[?]. As long as there is damaged DNA in the cell, it should not divide. If the damage can be repaired[?], the cell cycle can continue.
3. If the damage can not be repaired, the cell should initiate apoptosis, the programmed cell death, to remove the threat it poses for the greater good of the organism.

The first tumor suppressor protein discovered was the pRb protein in human retinoblastoma[?]. An important tumor suppressor is the p53 gene.

See also : Cancer -- signal transduction