Abstract P4-10-02: Impact of raloxifene adherence in breast cancer risk

Abstract

Abstract BACKGROUND: Raloxifene is a selective estrogen receptor modulator that has demonstrated to reduce breast cancer risk and reduce the incidence of vertebral fractures. Based on these effects, raloxifene is used as a risk reduction agent and to prevent osteoporosis in postmenopausal women. Little is known about the raloxifene adherence rates or the relationship between adherence and breast cancer incidence. METHODS: Women 60 years or older without a breast cancer history were identified in the MarketScan database (2008-2015). We identified women who received raloxifene by searching for prescription claims. Proportion of days covered (PDC) were calculated, adherence was defined as a PDC >80% in the first year after initial prescription claim. We identified factors associated with adherence. ICD-9 codes were used to identify incident cases of invasive breast cancer and cumulative incidence rates were calculated. A multivariable Cox model with propensity score method (matching variables included year of claim, age, comorbidities and family history of breast cancer) was used to evaluate the association between raloxifene adherence and breast cancer risk. All statistical tests were two-sided. RESULTS: A total of 16,179 women were included in the analysis. We identified that during the first year of treatment 6,716 (40.2%) women had a PDC >80% and thus were considered to be adherent. Factors associated with increased adherence included the use of generic drug, mail order of 90 days supply and family history of breast cancer (all p<0.001). Using propensity score matching, the 5 year-cumulative incidence of invasive breast cancer was 1.5% among those not adherent and 0.9% among those adherent to raloxifene (p=0.01). Similarly, the 9 year-cumulative rates were 3.6% and 1.9% respectively (p=0.01). After adjusting for potential confounders, patients that were adherent to raloxifene during the first year of treatment had a lower risk of invasive breast cancer compared to those that were non-adherent (HR=0.64; 95%CI 0.04-0.9). CONCLUSIONS: Among women 60 years of age or older receiving raloxifene, adherence to therapy was associated with lower risk of invasive breast cancer. Efforts to ensure adherence and compliance are crucial so patients can receive full benefit from this therapy. Citation Format: Chavez-MacGregor M, Lei X, Zhao H, Bevers TB, Brewster A, Giordano SH. Impact of raloxifene adherence in breast cancer risk [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-10-02.