Abstract A23: Plasma osteoprotegerin and breast cancer risk in BRCA1 and BRCA2 mutation carriers
Authors: Salmena Leonardo , Oden Lovisa , Kim Shana , Akbari Mohammad , Sun Ping , Narod Steven , Kotsopoulos Joanne 
Published: May 2019

Abstract
Background: There is emerging evidence to suggest that progesterone-mediated upregulation of the receptor activator of nuclear factor κ β (RANK)/RANK ligand (RANKL) signaling pathway plays a critical role in mammary gland epithelial cell proliferation, mammary stem cell expansion and carcinogenesis. Of relevance for women at a high risk of developing breast cancer due to an inherited BRCA mutation, are recent findings showing that circulating levels of osteoprotegerin (OPG) (an endogenous decoy receptor for RANKL and thus inhibitor of RANK/RANKL-mediated signaling) are lower in women with a BRCA1 or BRCA2 mutation compared to non-carriers. Whether low OPG concentrations contribute to the high breast cancer risk in this population is unknown. If so, a therapeutic intervention that mimics the action of OPG might be used for primary prevention. We evaluated the relationship between plasma OPG and breast cancer risk among women with a BRCA1 or BRCA2 mutation in a prospective study.
Methods: Baseline blood samples were available from 206 BRCA mutation carriers with no previous history of cancer. Plasma OPG concentrations were measured using a commercial enzyme-linked immunosorbent assay (ELISA) and categorized dichotomously as high vs. low based on the median of the entire cohort. The cumulative incidence of breast cancer by baseline plasma OPG concentration was estimated using Kaplan-Meier survival analysis.
Results: Over a mean follow-up period of 6.5 years (range 0.1-18.8 years), 18 incident cases of primary invasive breast cancer were observed in the cohort. Women who developed breast cancer had significantly lower mean baseline OPG concentrations (90.59 pg/ml [range 4.2-205.7 pg/ml]) compared to the OPG concentrations of women who did not develop breast cancer ((117.9 pg/ml [7.4-547.7]) (P = 0.04). BRCA mutation carriers with low baseline OPG concentrations (&lt; 95 pg/ml) had a significantly higher risk of developing breast cancer compared to those with high baseline OPG concentrations (≥95 pg/ml). After ten years of follow-up, the cumulative incidence of breast cancer among women with low OPG concentrations was 21% compared to 9% among women with high OPG concentrations (P-log rank test = 0.046). There was no evidence of effect modification by menopausal status or BRCA mutation type. After multivariate adjustment, women with high plasma OPG had a significantly decreased risk of developing breast cancer, compared to women with low OPG (HR = 0.25; 95%CI 0.08-0.78; P = 0.02).
Conclusions: Our preliminary data suggest that low OPG concentrations are associated with an increased risk of breast cancer in BRCA1 and BRCA2 mutation carriers. These data support the potential for targeting of the RANKL pathway as a plausible cancer prevention strategy among women with germline BRCA mutations. Additional analyses with a larger sample size are underway and may help inform strategies of personalized prevention. These findings will not only further our understanding of the progesterone/OPG/RANKL pathway in breast cancer development, but will improve our identification of high-risk populations that can be targeted by prevention options that are currently available (i.e., denosumab) to simultaneously prevent breast cancer development and maintain bone health (particularly after salpingo-oophorectomy).
Citation Format: Leonardo Salmena, Lovisa Oden, Shana Kim, Mohammad Akbari, Ping Sun, Steven Narod, Joanne Kotsopoulos. Plasma osteoprotegerin and breast cancer risk in BRCA1 and BRCA2 mutation carriers. [abstract]. In: Proceedings of the AACR Special Conference: Improving Cancer Risk Prediction for Prevention and Early Detection; Nov 16-19, 2016; Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(5 Suppl):Abstract nr A23.