Comparison of anastrozole versus tamoxifen as preoperative therapy in postmenopausal women with hormone receptor‐positive breast cancer

BACKGROUND The Pre‐Operative “Arimidex” Compared to Tamoxifen (PROACT) study was a randomized, multicenter study comparing anastrozole with tamoxifen as a preoperative treatment of postmenopausal women with large, operable (T2/3, N0‐2, M0), or potentially operable (T4b, N0‐2, M0) breast cancer. The effect of preoperative endocrine therapy in patients scheduled for mastectomy or with inoperable tumors at baseline was also investigated. METHODS Patients with hormone receptor‐positive breast cancer received anastrozole (n = 228) or tamoxifen (n = 223) with or without chemotherapy for 12 weeks before primary surgery. RESULTS Objective responses for anastrozole and tamoxifen occurred in 39.5% and 35.4% of patients, respectively (ultrasound measurements), and 50.0% and 46.2% of patients, respectively (caliper measurements). In hormonal therapy‐only patients (n = 314), feasible surgery at baseline improved after 3 months in 43.0% of patients receiving anastrozole and 30.8% receiving tamoxifen (P = .04). In the intent‐to‐treat population, improvement in feasible surgery at baseline to actual surgery at 3 months was found to be numerically higher in the anastrozole group compared with the tamoxifen group, although this difference did not reach significance. Drug‐related adverse events were reported in 20.2% and 18.1% of patients, respectively, in the anastrozole and tamoxifen groups. CONCLUSIONS Anastrozole is an effective and well‐tolerated preoperative therapy, producing clinically beneficial tumor downstaging and reductions in tumor volume. These effects enable more minimal surgical interventions in patients scheduled for mastectomy, and mastectomy in patients with previously inoperable tumors. Anastrozole appears to be at least as effective as tamoxifen in this setting, and more effective than tamoxifen in certain clinically relevant subgroups. Cancer 2006. © 2006 American Cancer Society. Preoperative anastrozole produced a numerically greater number of objective responses with respect to tumor size reduction compared with preoperative tamoxifen. The Pre‐Operative “Arimidex” Compared to Tamoxifen (PROACT) study demonstrated that anastrozole is an effective and well‐tolerated preoperative therapy that produces clinically beneficial tumor downstaging and reductions in tumor volume.