Abstract
BackgroundAnastrozole reduces breast cancer risk in women at high risk, but implementing preventive therapy in clinical practice is difficult. Here, we evaluate adherence to anastrozole in the International Breast Cancer Intervention Study (IBIS)-II prevention and ductal carcinoma in situ (DCIS) trials, and its association with early symptoms.Patients and methodsIn the prevention trial, 3864 postmenopausal women were randomized to placebo versus anastrozole. A total of 2980 postmenopausal women with DCIS were randomized to tamoxifen versus anastrozole. Adherence to trial medication was calculated using the Kaplan–Meier method and all P-values were two-sided.ResultsIn the prevention trial, adherence was 65.8% [anastrozole (65.7%) versus placebo (65.9%); HR = 0.97 (0.87–1.09), P = 0.6]. Adherence was lower for those reporting arthralgia in the placebo group (P = 0.02) or gynecological symptoms in the anastrozole group (P = 0.003), compared with those not reporting these symptoms at 6 months. In the DCIS study, adherence was 66.7% [anastrozole (67.5%) versus tamoxifen (65.8%); HR = 1.06 (0.94–1.20), P = 0.4]. Hot flashes were associated with greater adherence in the anastrozole arm (P = 0.02). In both studies, symptoms were mostly mild or moderately severe, and adherence decreased with increasing severity for most symptoms. Drop-outs were highest in the first 1.5 years of therapy in both trials.ConclusionsIn the IBIS-II prevention and DCIS trials, over two-thirds of women were adherent to therapy, with no differences by treatment groups. Participants who reported specific symptoms in the IBIS-II prevention trial had a small but significant effect on adherence, which strengthened as severity increased. Strategies to promote adherence should target the first year of preventive therapy.
Highlights
Breast cancer is the most frequent cancer among women worldwide, with an estimated 1.67 million new cancer cases diagnosed in 2012 [1] and the prevention of breast cancer is a recognized priority [2]
The following predictors were significantly associated with adherence in the univariate model: 60 years or older, hysterectomy, oophorectomy, natural menopause, and previous participation in the International Breast Cancer Intervention Study (IBIS)-I prevention trial
When adherence was investigated adjusted for all previous significant predictors, being older than 60 years of age [OR 1⁄4 1.17 (1.01– 1.34), P 1⁄4 0.03], not having had a hysterectomy [OR 1⁄4 0.75 (0.59–0.96), P 1⁄4 0.03], and previous participation in the IBIS-I trial [OR 1⁄4 1.38 (1.14–1.67), P 1⁄4 0.001] remained significant predictors for adherence
Summary
Breast cancer is the most frequent cancer among women worldwide, with an estimated 1.67 million new cancer cases diagnosed in 2012 [1] and the prevention of breast cancer is a recognized priority [2]. Preventive therapy for women at high risk of developing breast cancer or those with a diagnosis of ductal carcinoma in situ (DCIS) can reduce disease burden. Data from the International Breast Cancer Intervention Study II (IBIS-II) prevention trial show that women randomly assigned to receive anastrozole (1 mg/day) were over 50% less likely to be diagnosed with breast cancer compared with those taking a matching placebo [5]. Anastrozole reduces breast cancer risk in women at high risk, but implementing preventive therapy in clinical practice is difficult. We evaluate adherence to anastrozole in the International Breast Cancer Intervention Study (IBIS)-II prevention and ductal carcinoma in situ (DCIS) trials, and its association with early symptoms. Patients and methods: In the prevention trial, 3864 postmenopausal women were randomized to placebo versus anastrozole.
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