Reduced incidence of invasive breast cancer with raloxifene among women at increased coronary risk

Abstract

Background: In the Raloxifene Use for The Heart trial, 10 101 postmenopausal women with coronary heart disease (CHD) or multiple CHD risk factors were randomly assigned to 60 mg/d raloxifene or to placebo and followed for a median of 5.6 years. Raloxifene, a selective estrogen receptor modulator, was found to reduce the risk of invasive breast cancer and vertebral fractures but not the risk of cardiovascular events. Here, we provide further details about breast cancer incidence by tumor characteristics, duration of treatment, and subgroup.

Methods: Reported breast cancer was adjudicated by an independent committee based on medical records and pathology reports. The primary analyses used Cox proportional hazards models with time to first breast cancer as the outcome. Subgroup effects were analyzed using similar models with terms for treatment by subgroup. All statistical tests were two-sided.

Results: As previously reported, raloxifene reduced the incidence of invasive breast cancer by 44% (hazard ratio [HR] = 0.56; 95% confidence interval [CI] = 0.38 to 0.83; absolute risk reduction = 1.2 invasive breast cancers per 1000 women treated for 1 year). The lower incidence of invasive breast cancer reflected a 55% lower incidence of invasive estrogen receptor (ER)-positive tumors (HR = 0.45; 95% CI = 0.28 to 0.72). However, raloxifene treatment did not reduce the incidence of noninvasive breast cancer or of invasive ER-negative breast cancer. The reduced incidence of invasive breast cancer was similar across subgroups, including those defined by age, body mass index, family history of breast cancer, prior use of postmenopausal hormones, and 5-year estimated risk of invasive breast cancer.

Conclusion: Raloxifene reduces risk of invasive ER-positive breast cancer regardless of a woman's baseline breast cancer risk but does not reduce risk of noninvasive or ER-negative breast cancers. These results confirm those of the Multiple Outcomes of Raloxifene Evaluation, a previous randomized trial among women with osteoporosis.

Figure 1

Cumulative breast cancer incidence rates. A) invasive breast cancer, B) noninvasive breast cancer, C) invasive estrogen receptor (ER)–positive breast cancer, and D) invasive ER-negative breast cancer. The cumulative number of events and number of participants at risk are shown below each plot.

Figure 2

Invasive breast cancer (annualized percent) by baseline characteristics and treatment assignment. Hazard ratios (dots) and 95% confidence intervals (error bars) are from unadjusted Cox proportional hazards models, and P_interaction values are from Cox proportional hazards models that include an interaction term for subgroup and treatment effect. Diamond indicates the overall hazard ratio. BMI = body mass index; IBC = invasive breast cancer.