Abstract OT1-01-03: Impact of RANKL inhibition on tumor microenvironment of early-stage breast cancer, a pre-surgical trial

BACKGROUND: Receptor activator of NF-kB (RANK) and its ligand (RANKL) have a well-established role in osteoclast-driven bone remodeling, however RANK/RANKL expression can also be seen on mammary epithelial cells and immune cells (IC). In breast cancer (BC) mouse models, RANKL is a paracrine effector of the mitogenic activity of progesterone and inhibition of RANKL can attenuate development of BC as well as the incidence of metastases. Pre-clinical evidence demonstrates that RANKL exerts effects on IC such as regulatory T cells (Tregs) and tumor associated macrophages (TAMs) within the tumor microenvironment (TME), thereby promoting tumor progression and metastases. Clinical studies also support a deleterious role for these IC subsets specifically in breast cancer, with high density of either Tregs or TAMs associated with increased risk for distant recurrence. Despite this preclinical support for targeting the RANK/RANKL pathway, clinical trials in early stage BC have had discordant results regarding the clinical benefit of denosumab (RANKL antagonist). As such, it is of significant clinical relevance to identify a drug response signature following treatment as this may suggest biomarkers predictive of benefit from adjuvant denosumab. This window-of-opportunity study was designed to evaluate the pharmacodynamic biomarkers of RANKL inhibition, as well as denosumab’s impact on the TME in paired tumor specimens from patients with BC following treatment with denosumab. Defining the immunomodulatory effects of denosumab may additionally provide biologic rationale for synergistic combination with specific immunotherapy agents. TRIAL DESIGN: This study is a single-arm open label Phase 0 (pre-surgical/window of opportunity) trial. Following diagnostic core needle biopsy, patients receive one dose of denosumab 120 mg given subcutaneously prior to surgical resection. ELIGIBILITY CRITERIA: ≥18 years of age with histologically-confirmed invasive BC >1 cm by radiographic or clinical criteria with available tissue from the core biopsy and planned surgery. Patients are ineligible for this study if neoadjuvant therapy is being considered. STUDY OBJECTIVES: The primary objective is to identify pharmacodynamics markers of RANKL inhibition in early BC. Planned analyses include protein and transcriptomic analyses of known targets of RANKL and compare treatment effect in both RANK/RANKL+ and RANK/RANKL- BC. As a secondary objective, the effect of RANKL inhibition on host immune response will be assessed by comparing pre-treatment biopsy specimens and surgical excision specimens from patients treated with denosumab and untreated controls matched for BC subtype and menopausal status. Planned analyses include RANK/RANKL expression on IC subsets, enumeration of tumor infiltrating lymphocytes by HE 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT1-01-03.