In silico studies raised the possibility that farnesyltransferase inhibitors (FTIs) may have antitumoral effects on KRAS mutant cancer cells. Accordingly, we have tested FTIs (tipifarnib and lonafarnib) in G12C mutant human cancer cell lines in vitro and in vivo. We have discovered that the combination of the two drugs has a synergistic antitumoral effect. Next, we have tested FTIs on G12D mutant human cancer cell lines and found that the combination has antitumoral effect in various preclinical cancer models. At last, we have also tested FTIs on G12V mutant human cancer cells and again we have detected antitumoral effects. We suggest that FTIs may have clinical relevance outside the HRAS mutant cancers.