Abstract
Proto-oncogenes are cellular genes that are expressed during normal growth and developmental processes. Altered versions of normal proto-oncogenes have been implicated in the development of human neoplasia. In this report, we show the detection of activated proto-oncogenes in various spontaneous and chemically induced rodent tumors. The majority of activated proto-oncogenes found in these tumors are members of the ras gene family and have been activated by a point mutation. Characterization of the activating mutation may be useful in determining whether this proto-oncogene was activated by direct interaction of the chemical with the DNA. Comparison of activating lesions in spontaneous versus chemically induced tumors should be helpful in determining whether the chemical acts via a genotoxic or a nongenotoxic mechanism. All of this information may be helpful in the assessment of potential carcinogenic hazards of human exposure to chemicals.