Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II) an international, double-blind, randomised placebo-controlled trial

SUMMARY: NOLVADEX® (Tamoxifen) is a Selective Estrogen Receptor Modulator (SERM), approved by the FDA to also reduce the incidence of breast cancer in women considered to be at high risk (ChemoPrevention). This agent however has been linked to endometrial cancer and thromboembolic phenomenon in some women. ARIMIDEX® is a non-steroidal Aromatase Inhibitor proven to be more efficacious than NOLVADEX® both in metastatic and adjuvant settings. Similar to NOLVADEX®, ARIMIDEX® also prevents the occurrence of new primary tumors in the contralateral breast, in postmenopausal females. With this background, the International Breast Cancer Intervention Study (IBIS) -II trial enrolled 3864 postmenopausal women considered to be at increased risk of breast cancer and randomized them to receive either ARIMIDEX® (Anastrazole) 1 mg QD (N=1920) or Placebo QD (N=1944)for 5 years. Patients were considered to be at high risk if they had a family history of breast cancer, atypical ductal hyperplasia, lobular carcinoma in-situ or dense breast tissue. The median age was 59 years. The primary end point was histologically confirmed Invasive breast cancer or Ductal Carcinoma In- Situ. At a median follow up of 5 years, the incidence of breast cancer in the ARIMIDEX® group was 2% and in the placebo group was 4%. The predicted cumulative incidence of breast cancer after 7 years was 2.8% in the ARIMIDEX® group and 5.6% in the placebo group (HR=0.47; P<0.0001). This represented a 53% reduction in the risk of breast cancer. The adverse events were comparable in both groups with slight increase in the musculoskeletal and vasomotor events noted in the ARIMIDEX® group. The authors concluded that ARIMIDEX® reduced the risk of primary breast cancer by more than 50% in high risk postmenopausal women. Other unrelated studies have shown that acceptance of breast cancer prevention with medications (ChemoPrevention) appeared to be related to education and income, putting emphasis on education and adequate counseling of women, considered to be at high risk. Cuzick J, Sestak I, Forbes JF, et al. The Lancet, Early Online Publication, 12 December 2013