289P Results of the window-of-opportunity clinical trial D-BIOMARK: Study of biomarkers of the antitumor activity of denosumab and its role as a modulator of the immune response in early breast cancer

Inhibitors of the Receptor Activator of NFkB (RANK) pathway, such as denosumab, have been shown to prevent breast cancer (BC) in preclinical models by reducing proliferation and tumor cell survival. Recent studies suggest that RANK pathway inhibition enhances the anti-tumor immune response. This study aimed to evaluate the antiproliferative, proapoptotic (primary endpoints), and immunomodulatory activity (exploratory endpoint) of denosumab in early BC. D-BIOMARK study (NCT03691311) was a randomized window-of-opportunity trial designed to evaluate the biological effects of single-agent denosumab in early BC. Sixty patients with early HER2-negative BC were enrolled, 2:1 randomization to experimental (two doses of 120mg of denosumab separated by 7 days before surgery) or control (no treatment) group. Paired samples (core-biopsy and surgical specimen) were obtained from each patient for comparison of Ki67 (proliferation), Cleaved Caspase-3 (cell survival), and tumor infiltrating lymphocytes (TILS) according to international guidelines. Pre vs. post values were compared using a paired t-test. A total of 58 evaluable patients were analyzed, 10 with triple-negative breast cancer (TNBC), 27 premenopausal and 31 postmenopausal. Denosumab reduced free RANKL (sRANK) levels in patient’s serum but did not reduce tumor cell survival or proliferation. Denosumab increased TILS in all patients, except TNBC (n=6) while differences in the control group did not reach statistical significance. When considering clinically significant increases in TILS (5% or 10%), no differences were found between both groups. No associations were found between basal sRANKL and an increase in TILS.Table: 289PResponse variableMean PreMean PostControl p-valueMean PreMean PostExperimental p-valuesRANKL pg/ml N=580.100.120.250.010.00<0.01Ki-67 % N=5824.5229.190.0520.5925.240.01CLEAVED-CASPASE 3 H-score N=581.662.240.052.561.980.24TILS % N=587.4212.240.067.3512.94<0.01TILS % within Luminal BC N=488.1711.780.186.1310.800.01TILS % within TNBC N=104.25014.2500.2413.66724.0000.08TILS % within premenopausal patients with luminal BC N=2610.6812.600.647.3112.730.05TILS within postmenopausal patients with luminal BC =228.1711.770.064.878.750.04 Open table in a new tab . Denosumab did not affect tumor cell survival nor proliferation in early BC but may have an immunomodulatory effect that warrants further investigation.