Cancer is a genetic disorder in which the normal control of cell growth is lost. Cancer genetics is now one of the fastest expanding medical specialties. At the molecular level, cancer is caused by mutation(s) in DNA, which result in aberrant cell proliferation. Most of these mutations are acquired and occur in somatic cells. However, some people inherit mutation(s) in the germline. The mutation(s) occur in two classes of cellular genes: oncogenes and tumor suppressor genes. Transformation of proto-oncogene to oncogene is the result of gain in function through: Under normal conditions, tumor suppressor genes regulate cellular differentiation and suppression of proliferation. Mutations in these genes result in unchecked cellular proliferation resulting in tumors with abnormal cell cycles and tumor proliferation. The tumor suppressor genes contribute to cancer by the inactivating of loss of function mutation.