A potent, selective, nonpeptidomimetic inhibitor of farnesyl protein transferase (FPT), an enzyme involved in protein processing (farnesylation) for signal transduction. Displays significant antitumor effects in vivo.  Tipifarnib competitively inhibits the farnesylation of lamin B (IC₅₀ = 0.86 nM) and K-RasB (IC₅₀ = 7.9 nM) peptide substrates and inhibits the cell growth of ~75% of a panel of 53 human tumor cell lines tested.