Lonafarnib is a synthetic tricyclic derivative of carboxamide with antineoplastic properties. Lonarfanib binds to and inhibits farnesyl transferase, an enzyme involved in the post-translational modification and activation of Ras proteins. Ras proteins participate in numerous signalling pathways (proliferation, cytoskeletal organization), and play an important role in oncogenesis. Mutated ras proteins have been found in a wide range of human cancers.