Anastrozole and the Prevention of Breast Cancer

Andrew M. Kaunitz, MD

This aromatase inhibitor was more effective than previously reported for tamoxifen and raloxifene — but in the absence of a clear mortality benefit, adverse effects loom large.

Although the selective estrogen receptor modulators (SERMs) tamoxifen and raloxifene are the only agents approved for preventing breast cancer in high-risk women, earlier reports have suggested that aromatase inhibitors (AIs) may be more effective than SERMs for chemoprophylaxis. In an international, partially manufacturer-funded trial, investigators assessed the efficacy and safety of the AI anastrozole (1 mg daily for 5 years) versus placebo in postmenopausal women with excess risk for breast cancer.

Among 3864 participants (median age at baseline, 60), significantly fewer breast cancers overall were diagnosed in the anastrozole group than the placebo group (hazard ratio, 0.47; P<0.0001), although anastrozole did not significantly lower incidence of receptor-negative invasive tumors. The authors estimated that 36 women would need to be treated with the AI to prevent one cancer in 7 years of follow-up. Overall and cause-specific death rates were similar (1%) in both study groups. Arthralgias, carpal tunnel syndrome, vasomotor symptoms, vaginal dryness, hypertension, and dry eyes were significantly more common in the AI group; pelvic prolapse and vulvovaginal pruritis were less common. Rates of fractures and cardiovascular events were similar in both groups.

Citation(s):

Cuzick J et al. Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II): An international, double-blind, randomised placebo-controlled trial. Lancet 2013 Dec 12; [e-pub ahead of print].

Cameron DA.Breast cancer chemoprevention: Little progress in practice? Lancet 2013 Dec 12; [e-pub ahead of print].