Abstract P6-09-01: In primary, non-metastatic breast cancer patients, increased serum levels of RANKL significantly correlate with tumor cell spread to the bone and the occurrence of bone metastasis whereas high levels of its soluble decoy receptor osteoprotegerin predict poor survival
Authors: Bittner A-K , Goebel A , Hoffmann O , Rauner M , Hofbauer LC , Kimmig R , Kasimir-Bauer S , Rachner TD 
Published: May 2019

Abstract
Background: Receptor activator of nuclear factor kappa-B ligand (RANKL) is an essential protein for osteoclast regulation and its activity is controlled by its soluble decoy receptor osteoprotegerin (OPG). RANKL has been associated with benign as well as malignant bone disease and there is increasing evidence that RANKL may also directly affect breast cancer (BC) progression and metastasis to the bone. Here we assessed serum concentrations of RANKL and OPG in 509 patients with primary, non-metastatic BC and correlated the results with clinical parameters including the presence of disseminated tumor cells (DTCs) in the bone marrow (BM), survival and the risk of developing metastatic disease.
Patients and Methods: Patients with first diagnosis of BC between Aug 2006 and Dec 2009 were included in our study. BM sampling was performed before surgery in an adjuvant setting and two BM aspirates were analyzed for DTCs using density centrifugation followed by immunocytochemistry applying the pan-cytokeratin antibody A45-B/B3. Blood was collected from each patient and sRANKL and OPG levels in the serum were measured by ELISA (Biomedica, Vienna, Austria). Results: Mean serum values for RANKL and OPG were 0.23±0.20 pmol/l and 4.24±1.70 pmol/l, respectively. RANKL levels were significantly lower in women above the age of 60 (p&lt;0.0001) and RANKL/OPG ratios were higher in patients with lymph node involvement (p&lt;0.05). High OPG levels were associated with a higher risk of death from BC (HR 1.94 95%CI 1.23-3.07; p=0.005) and multivariate analyses revealed OPG to be an independent prognostic marker for BC specific survival (p=0.035). DTCs were detected in 207/507 (41%) patients and RANKL levels were 33% higher in DTC-positive patients (p&lt;0.0001). Interestingly, in DTC-negative patients, high RANKL levels were associated with a significantly better BC specific survival compared to low levels (HR 0.524; 95%CI 0.30-0.95; p=0.04). RANKL serum levels were significantly enhanced in patients that developed bone metastases (p=0.01) and patients in the highest quartile of RANKL had a significantly increased risk of developing bone metastases compared to those in the lowest RANKL quartile (HR 4.62, 95%CI 1.49-14.34, p=0.03). Conclusion: Increased OPG levels indicated poor survival and high RANKL significantly associated with an increased risk of developing bone metastases while indicating a positive prognostic marker in DTC-negative patients. These findings warrant further investigation as it may provide a rational for novel diagnostic or therapeutic approaches.
Citation Format: Bittner A-K, Goebel A, Hoffmann O, Rauner M, Hofbauer LC, Kimmig R, Kasimir-Bauer S, Rachner TD. In primary, non-metastatic breast cancer patients, increased serum levels of RANKL significantly correlate with tumor cell spread to the bone and the occurrence of bone metastasis whereas high levels of its soluble decoy receptor osteoprotegerin predict poor survival [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-09-01.