A tumor suppressor gene directs the production of a protein that is part of the system that regulates cell division. The tumor suppressor protein plays a role in keeping cell division in check. When mutated, a tumor suppressor gene is unable to do its job, and as a result uncontrolled cell growth may occur. This may contribute to the development of a cancer.
Within our genome is a class of genes called tumor suppressor genes. These genes make proteins that act like brakes within the cell, and when they're turned on they actually prevent the cell from dividing. However, if a tumor suppressor gene is lost or mutated in a very specific way so that it loses its activity, the cell can then start to divide uncontrollably, and this contributes to the development of cancer. So the inactivation of tumor suppressor genes is one type of genetic alteration that contributes to tumor genesis. "Tumor genesis" is the technical term for the development of cancer.- Daphne W. Bell, Ph.D.