The accumulation of genetic damage in the forms of activated proto-oncogenes and inactivated tumor-suppressor genes is the driving force in the evolution of a normal cell to a malignant cell. For example, both the activation of ras oncogenes and the inactivation of several suppressor genes, including p53, have been observed in the development of human colon and lung tumors. Point mutations in k...

The study of oncogenic viruses led to the discovery that transforming retroviruses contain oncogenes homologous with and/or derived from cellular proto-oncogenes. In humans malignant transformation is often the result of the activation of proto-oncogenes. Normal proto-oncogenes can be activated to transforming proto-oncogenes by a variety of mechanisms including point mutation, translocation an...