Abstract 2162: Prior bone health history in breast cancer patients on aromatase inhibitors

Abstract

Abstract Background: Aromatase inhibitors (AIs) have been replacing tamoxifen (TAM) as adjuvant hormonal therapy (HT) for hormone receptor-positive, postmenopausal breast cancer (BC). AIs are known for their adverse effects on bone health, yet bone health history among AI users before BC diagnosis is unknown, which may impact fracture risk after AI therapy. In a cross-sectional analysis of a prospective cohort of BC patients on HT, we describe prior history of osteoporosis and fracture before BC diagnosis among AI users compared with TAM users. Methods: A total of 3280 women diagnosed with invasive BC from 2005-2013 and initially treated with AI or TAM were identified from an ongoing prospective cohort study at Kaiser Permanente Northern California (KPNC). Data on baseline demographic and lifestyle factors came from in-person interviews about two months post-diagnosis. Information on BC diagnosis and treatment, HT, and prior bone health history including bisphosphonate (BP) use was obtained from the KPNC cancer registry and clinical databases. Using age- and race-adjusted logistic regression, we examined the association of lifestyle and clinical factors at BC diagnosis with prior history of 1) osteoporosis, 2) any fracture (excluding head, face, fingers, toes), and 3) any major fracture (hip, spine, humerus, wrist). Results: Compared with initial TAM users (n=1140), initial AI users (n=2140) were more likely to be older (mean 64.5 y vs. 50.5 y) and obese (38% vs. 26%), yet less likely to have had chemotherapy (36% vs. 51%). AI users were more likely to have a prior history of osteoporosis (n=164, 7.7% vs. n=62, 5.4%, age-adjusted p<0.05), any fracture (n=356, 16.7% vs. n=92, 8.1%), and major fracture (n=104, 4.9% vs. n=22, 2.0%), yet the latter two were not significant after age adjustment. Among initial AI users, being ≥70 y (OR=5.8; 95% CI: 3.5, 9.5) and Asian (OR=1.9; 95% CI: 1.2, 3.2) were each associated with prior osteoporosis, whereas increasing BMI (obese OR=0.4; 95% CI: 0.2, 0.6) was associated with lower odds. Older age and prior osteoporosis were each related to higher odds of any prior fracture, yet the association with osteoporosis was not observed after further adjustment for prior BP use. Being Asian (OR=0.5; 95% CI: 0.3, 0.8) and light alcohol intake (≤median 0.84 g/day OR=0.7; 95% CI: 0.5, 1.0) were related to lower odds of any fracture. Odds of major fracture were similar yet attenuated with wide CIs. However, any moderate-vigorous physical activity was associated with reduced odds of major fracture (≤median 21.1 MET-hrs/wk OR=0.3; 95% CI: 0.2, 0.6; >median OR=0.4; 95% CI: 0.2, 0.7). Discussion: This descriptive analysis is one of the first to characterize AI users and risk factors for prior bone morbidity before BC diagnosis. In the future, this study will evaluate the impact of AIs on risk of subsequent bone outcomes and examine lifestyle, molecular, and genetic risk factors for AI-induced fractures. Funded by R01 CA166701 and R01 CA105274. Citation Format: Marilyn L. Kwan, Joan C. Lo, Li Tang, Cecile Laurent, Janise M. Roh, Malini Chandra, Theresa E. Hahn, Chi-Chen Hong, Lara Sucheston-Campbell, Dawn L. Hershman, Bette J. Caan, Charles P. Quesenberry, Barbara Sternfeld, Christine B. Ambrosone, Lawrence H. Kushi, Song Yao. Prior bone health history in breast cancer patients on aromatase inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2162. doi:10.1158/1538-7445.AM2014-2162