The present invention relates to methods and compositions for the specific inhibition of kinase suppressor of Ras (KSR). In particular, the invention provides genetic approaches and nucleic acids for the specific inhibition of KSR, particularly of KSR expression. The invention relates to antisense oligonucleotides and the expression of nucleic acid which is substantially complementary to KSR RNA. Oligonucleotide and nucleic acid compositions are provided. The invention provides methods to inhibit KSR, including inhibition of KSR expression. Methods for blocking gf Ras mediated tumorigenesis, metastasis, and for cancer therapy are provided. Methods for conferring radiosensitivity to cells are also provided.