The intensive study of molecular events leading to cellular transformation in tissue culture or in intact organisms culminated in the identification of 100 or more genes that can be defined as oncogenes or tumor suppressor genes. Functionally, these genes can be divided into several classes, each involved in a different step in transmission of signals from the exterior of the cell to the nucleus. The first oncogenes to be biochemically character- ized included membrane receptors for growth factors, growth factors themselves, protein kinases or small GTP binding proteins involved in signal...

The intensive study of molecular events leading to cellular transformation in tissue culture or in intact organisms culminated in the identification of 100 or more genes that can be defined as oncogenes or tumor suppressor genes. Functionally, these genes can be divided into several classes, each involved in a different step in transmission of signals from the exterior of the cell to the nucleus. The first oncogenes to be biochemically character- ized included membrane receptors for growth factors, growth factors themselves, protein kinases or small GTP binding proteins involved in signal...