Farnesyltransferase (Ftase) was identified by gene-expression profiling and by preclinical evaluation in in vitro and in vivo mantle cell lymphoma (MCL) models as a rational therapeutic target in MCL, one of the most refractory B-cell lymphomas. We conducted a multicenter phase II study of a potent Ftase inhibitor, tipifarnib, in patients with relapsed or refractory MCL.