In the last few years considerable progress has been made in our understanding of molecular oncology and we are beginning to see how this understanding can be translated into strategies for treatment or prevention. It is now widely recognized that tumor suppressor genes play an important role in the development of tumors and that oncogene mutation represents only one mechanism which leads to cancer. In their seminal study of colon cancer, Vogelstein and co-workers were able to identify several genetic events, notably activation of a dominant oncogene (ras) and inactivation of several tumor suppressor genes including p53 and DCC that contribute to cancer development and progression. These events occur in clonal populations of adenoma cells. Whether products of tumor suppressor genes and oncogenes interact with each other is not yet known with certainty.