0All genes whose epigenetic and genetic changes contribute to the causation of cancer is described as cancer-critical genes. These genes may be involved in the following processes-
1. Cell cycle progression (e.g. Rb, myc)
2. Differentiation process (e.g. Hh, apc)
3. DNA repair (e.g. Atm, Brca)
4. Cell death (e.g. Bcl-2)
Cancer critical genes are grouped into two broad classes, according to whether the cancer risk arises from a gain-of-function mutation of a gene or loss-of-function mutation. Genes for which a gain-of-function mutation drives a cell towards cancer, are called proto-oncogenes, Whereas the genes for which a loss-of-function mutation creates the cancer are called tumour suppressor genes.
Mutation of a critical cancer gene can be either dominant or recessive. Again in function mutation in a single copy of proto-oncogene can drive a cell towards cancer. On the other hand, cancer causing mutation of tumour suppressor genes is generally recessive. It means both copies of the normal gene must be removed or inactivated in the diploid somatic cell before an effect is seen.
