Abstract P6-08-13: Statins and breast cancer recurrence: A population-based case-control study
Authors: Vandermeer ML , Francisco MC , Richert-Boe KE , Jenkins CL , Weinmann S 
Published: February 2018

Abstract
Background: Breast cancer is the most common cancer among women and a significant number of women experience recurrence. Statins, drugs for lowering cholesterol, were introduced in 1987, and by 2011-12, 27.9% of U.S. adults over the age of 40 reported using cholesterol-lowering medication. Statins may impact other diseases, beyond cardiovascular disease, including cancer. Statin use and breast cancer recurrence or disease-free survival has previously been explored in 8 cohort studies and 1 case-control study with mixed results.
Methods: We designed a nested case-control study with Kaiser Permanente members in NW Oregon and SW Washington to examine the association between statins and breast cancer recurrence.
All subjects were women diagnosed with invasive breast cancer from 1980-2010. Subjects were KPNW health plan members at diagnosis, had local or regional stage cancer, were ER and/or PR positive, and were treated with tamoxifen for 180 days or more. Cases had breast cancer recurrence validated by medical record review. Controls were matched on race, SEER stage, age at diagnosis, year of diagnosis and pattern of health plan membership, and were recurrence-free for at least 12 months longer than their matched case (up to 3:1 match). The index date was the recurrence date for the case and the date for an equivalent period after diagnosis for the matched control. We collected data from medical records and from pharmacy, laboratory, tumor registry, and membership health plan databases.
We performed bivariate analysis to look at characteristics associated with recurrence. A priori, we identified potential confounding variables based on literature review and clinical knowledge. Using multivariable logistic regression analysis, we assessed statin use in relation to breast cancer recurrence, accounting for factors that may alter the association.
Results: We identified 306 cases with breast cancer recurrence and 679 matched controls. Thirty-five cases (11.4%) and 67 controls (9.9%) were prescribed statins at any time between their breast cancer diagnosis and index date. Nearly everyone on statins was prescribed lipophilic statins (99%). We calculated dose equivalents for all statins, using 20 mg of simvastatin as one dose. Among those who took statins, the average number of equivalent doses per day after diagnosis was 1.20 (1.19 for cases; 1.21 for controls) and the average duration of taking statins between diagnosis and recurrence was 2.65 years (2.75 for cases; 2.59 for controls). In our preliminary conditional analysis, we found that post-diagnostic statin use was not associated with a decreased odds of breast cancer recurrence (OR 1.37, 95% CI: 0.79-2.36) after adjusting for age, year of diagnosis, race, BMI, menopause status, tamoxifen use, type of surgery, treatment, smoking history, Charlson score, AJCC summary stage, and Nottingham grade.
Conclusions: While other studies have reported that statins may be associated with decreased odds of breast cancer recurrence, our preliminary multivariable analyses that looked at any statin use between diagnosis and index date do not support those results.
Citation Format: Vandermeer ML, Francisco MC, Richert-Boe KE, Jenkins CL, Weinmann S. Statins and breast cancer recurrence: A population-based case-control study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P6-08-13.