Abstract P6-08-12: Understanding the etiology of osteopenia and osteoporosis in young breast cancer survivors compared to cancer-free women

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Abstract Background: Our group previously reported that young breast cancer (BC) survivors have a higher risk of osteopenia/osteoporosis compared to their cancer-free peers. In order to develop successful interventions we need to understand the major contributing factors. Therefore, we investigated bone loss in young BC survivors by age at diagnosis, tumor characteristics and BC treatment compared to their cancer-free peers. Methods: We studied 775 women (211 BC survivors, 564 cancer-free) with familial risk of breast and/or ovarian cancer in the Breast and Ovarian Surveillance Service (BOSS) cohort at Johns Hopkins. Survivors were diagnosed with stage 0-III BC <5 years prior to enrollment. The comparison group was cancer-free women at enrollment. Osteopenia and osteoporosis were ascertained based on self-reported physician diagnosis in baseline and follow-up questionnaires. Prevalent cases of osteopenia or osteoporosis were excluded. Multivariable (MV)-adjusted Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of osteopenia and/or osteoporosis among BC survivors compared to cancer-free women. BC survivors were stratified by age at diagnosis, estrogen-receptor (ER) tumor status, and BC treatment. MV models were adjusted for age, menopausal status, body mass index, physical activity, smoking, alcohol use, hormone replacement therapy and early oophorectomy. Results: Mean time from BC diagnosis to enrollment was 1.4 years for survivors and mean age at BC diagnosis was 47 years. At baseline, BC survivors were more likely to be slightly older, postmenopausal, and current vitamin D users and less likely to have had an early bilateral oophorectomy compared to cancer-free women. During a mean follow-up time of 5.7 years, 66% of BC survivors and 54% of cancer-free women reported having ≥1 bone density exam and 112 incident cases of osteopenia/osteoporosis were identified (75% osteopenia only). BC survivors diagnosed at age ≤50 years had a 2-fold increased risk of osteopenia/osteoporosis compared to cancer-free women (HR=2.05, 95% CI=1.24-3.40). Risk of bone loss was similar among survivors with ER-positive tumors compared to cancer-free women (HR=2.04, 95% CI=1.30-3.22). No association was observed for BC survivors treated with tamoxifen only or chemotherapy only. BC survivors treated with aromatase inhibitors (AIs) only had almost 3-fold increased risk of osteopenia/osteoporosis compared to cancer-free women (HR=2.92, 95% CI=1.38-6.17). BC survivors treated with chemotherapy + tamoxifen and chemotherapy + AIs had over 2- and 4-fold increased risk of osteopenia/osteoporosis compared to cancer-free women (HR=2.28, 95% CI=1.04-5.00; HR=4.09, 95% CI=1.99-8.42, respectively). Results suggest that risk of bone loss was highest within 5 years after BC diagnosis. Conclusion: Our results demonstrate that osteopenia/osteoporosis incidence is higher in BC survivors compared to cancer-free women and risk varies by age at diagnosis, ER-status and BC treatment. Our findings provide support for a baseline evaluation of bone density close to diagnosis in BC survivors with familial risk. Future studies are needed to address the frequency of monitoring among specific age and treatment groups. Citation Format: Ramin CA, May BJ, Roden RBS, McCullough M, Armstrong DK, Visvanathan K. Understanding the etiology of osteopenia and osteoporosis in young breast cancer survivors compared to cancer-free women [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 P6-08-12.