Recent progress in the field of oncogenes has produced valuable information concerning the molecular and cellular biology of the cancer cell and provided a tool to investigate the process of carcinogenesis. Some oncogenes such as the ras, myc, erbB-2 and abl have been extensively investigated in the progression of carcinogenesis in several types of human tumors. The p53 tumor suppressor gene has recently been shown to play the role of "molecular policeman," and is obviously important in the development of many tumors, as mutations in this gene are the most common genetic abnormalities found in all neoplasias. In certain cases the incidence of aberrant gene expression and genetic alterations of oncogenes and tumor suppressor genes have been shown to be important in the progression of these cancers and may be of use as prognostic indicators and form the basis for a successful therapy.