A phase II, randomized, blinded study of the farnesyltransferase inhibitor tipifarnib combined with letrozole in the treatment of advanced breast cancer after antiestrogen therapy

Background This study assessed the clinical efficacy of the farnesyltransferase inhibitor, tipifarnib, combined with letrozole in patients with advanced breast cancer and disease progression following antiestrogen therapy. Patients and methods Postmenopausal women with estrogen-receptor-positive advanced breast cancer that had progressed after tamoxifen were given 2.5 mg letrozole once daily and were randomly assigned (2:1) to tipifarnib 300 mg (TL) or placebo (L) twice daily for 21 consecutive days in 28-day cycles. The primary endpoint was objective response rate. Results Of 120 patients treated with TL (n = 80) or L (n = 40), 113 were evaluable for response. Objective response rate was 30% (95% CI; 20-41%) for TL and 38% (95% CI; 23-55%) for L. There was no significant difference in response duration, time to disease progression or survival. Clinical benefit rates were 49% (TL) and 62% (L). Tipifarnib was generally well tolerated; a higher incidence of drug-related asymptomatic grade 3/4 neutropenia was observed for TL (18%) than for L (0%). Tipifarnib population pharmacokinetics were similar to previous studies, with no significant difference in trough letrozole concentrations between the TL and L groups. Conclusions Adding tipifarnib to letrozole did not improve objective response rate in this population of patients with advanced breast cancer.