TNFSF11 and breast cancer: Furthermore, we (and others) have hypothesized that quantification of circulating osteoprotegerin (OPG), the decoy receptor of RANK-ligand (RANKL), may serve as a potential biomarker of BRCA1-associated breast cancer risk that may not only improve upon current risk prediction models, stratifying women at the highest risk of developing the disease, but may further identify those who may be targets for anti-RANKL chemoprevention.