Who Benefits from Strategies to Prevent Breast Cancer?

Strategies using tamoxifen, raloxifene, or aromatase inhibitors to reduce risks for developing breast cancer in high-risk women have been available for two decades, but relatively few eligible women choose to use these drugs. The eligibility criteria for chemoprevention trials can identify a very large potential population of women for these strategies, but identifying the women who are most likely to benefit remains a challenge. Now, investigators address this issue by reexamining data from the placebo-controlled, manufacturer-funded IBIS-II prevention study, which demonstrated that taking anastrozole for 5 years was associated with a 50% reduction in the odds of developing invasive breast cancer in 3864 postmenopausal women (age range, 40–70; median follow-up, 131 months).

In this preplanned case–control study, investigators analyzed baseline blood samples to determine the ratio of estradiol to sex-hormone–binding globulin (SHBG) and the ratio's effect on the development of breast cancers, including ductal carcinoma in situ, in 212 anastrozole recipients (72 women who developed breast cancer, 140 controls) and 416 placebo recipients (142 cases, 274 controls). Estradiol–SHBG ratio results were separated into quartiles. In the placebo group only, as baseline estradiol–SHBG ratios increased, so did breast cancer risks (P=0.0033). In a post hoc analysis, a relative benefit of anastrozole over placebo was seen in women with ratios in quartiles 2 to 4.