This section identifies that a cancer gene alters the normal functioning of a protein, and there are three major categories of cancer genes.

Cancer gene types A cancer gene alters the normal functioning of a protein. There are three major categories of cancer genes. Bert Vogelstein, M.D. is a Howard Hughes Medical Institute Investigator and the Clayton Professor of Oncology and Pathology at Johns Hopkins University. His research focuses on the identification and characterization of genes that cause colon cancer. This has led to the discovery of the APC gene – the "gatekeeper" in colon cancer development. “Cancer is in essence a genetic disease. It's caused by mutations of genes and there are three kinds, three types of genes, that contribute to cancer. The first is called oncogenes. These are genes that normally signal cells to grow. And when an oncogene is mutated, the cell continues to grow even though normally it wouldn't. A good analogy for an oncogene is the accelerator in a car. And a mutation in an oncogene is like having accelerator stuck to the floor, car keeps going even though the driver takes his or her foot off it. Cell keeps growing even though it's not receiving the signals that would normally drive cell growth. Second class is called tumor suppressor genes and these are the brakes of the cell. And just as cars have more than one brake, they have a foot brake and they have a hand brake and you can even take the keys out of the ignition if all else fails. Cells have more than one brake, more than one tumor suppressor gene. And it's the combination of mutations in oncogenes and tumor suppressor genes, sequential accumulation of those mutations, that eventually results in a full-blown cancer. Now there's one other class of genes, which contributes to cancer, this class is called stability genes. They don't directly control cell birth or cell death, that is they don't directly impact net cell growth. What they do is simply control the rate of mutation. So if one has a defective stability gene, then all genes are mutated more frequently, including oncogenes and tumor suppressor genes, so the whole process is accelerated. And a good analogy for a defective stability gene is having an inept mechanic work on your car. It keeps getting worse.” “Cancer is in essence a genetic disease. But it's really quite different than all the other genetic diseases that people usually think of when they think about a genetic disease. For instance cystic fibrosis: cystic fibrosis is always caused by a mutation in a single gene. People who get that mutation generally get very similar symptoms. One mutation gives you the disease. Cancer's not like that. No single mutation results in cancer. It's an accumulation of mutations in both these brakes and in the accelerators. You have to dismantle, basically, many of the controlling elements in the cell, to get to a cancer. If you just dismantle a few of them you might get a benign tumor, but you won't get a cancer. It's only when all of these pathways, or many of them, are inactivated that a cancer results. So it wouldn't be correct to say that a given mutation and a given gene causes cancer, what you can say is a given mutation contributes to the development of cancer.”

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