Abstract 2206: Pilot phase I clinical trial of RANKL inhibition and breast tissue gene expression in high-risk premenopausal women with dense breasts
Authors: Waters Michael , Jayachandran Kay , Bennet Debbie , Zhang Jin , Weilbaecher Katherine , Hagemann Ian S. , Colditz Graham A. , Appleton Catherine M. , Toriola Adetunji T. 
Published: June 2022

Abstract
Background: Identifying pathways that can be targeted to reduce breast density and breast cancer incidence is an unmet need, especially in premenopausal women. Receptor activator of nuclear factor-κB ligand (RANKL) signaling mediates the major proliferative response of mammary epithelium to progesterone and is positively associated with breast density but there are no clinical trial data on the impact of RANKL inhibition on breast tissue markers in women with dense breasts. We, therefore, determined the impact of RANKL inhibition on breast tissue gene expression in high-risk premenopausal women with dense breasts.
Study design: Pilot phase I clinical trial of 9 healthy high-risk pre-menopausal women (≥35 years of age) with dense breasts performed at Washington University School of Medicine, St. Louis, MO from July 2018-December 2018. Fifty-five percent of participants had a positive family history of breast cancer in a first degree relative.
Intervention: Participants were given a single dose of subcutaneous RANKL antibody, denosumab (60mg), at baseline (Day 1). On the same day, prior to the denosumab injection, participants had an ultrasound guided core needle biopsy and a blood draw. All study participants returned for repeat core needle biopsy and blood draw after 60 days (Day 60).
Outcome Measures: Changes in breast tissue gene expression between Day 1 and Day 60 with a focus on immune/inflammatory and hormone markers. Gene expression was profiled using NanoString nCounter platform. We performed pathway enrichment analysis and used Cell Maker Enrichment library from EnrichR to identify differentially expressed genes. Genes with a p-value&lt;0.05 on differential expression analysis were considered statistically significant for utilization in pathway enrichment analysis. Libraries utilized for pathway enrichment using the EnrichR platform included the ChEA transcription factor library, GO Biological Process library, and Cellular Components library.
Results: Macrophage markers, including CCR5, CD86, CD300A, and CD84 and targets downstream of IRF8: (p-value =4.73e-7), neutrophil degranulation/neutrophil activation in the immune response (p-value=6.0e-21), and the secretory granule membrane pathways (p-value=2.4e-14) were downregulated in breast tissues on Day 60. Pathways involved in progesterone metabolism (p-value=0.0003), estrogen response (p-value=0.0014) and fatty acid metabolism, (p-value=0.0001) were significantly upregulated on Day 60. Specifically, genes involved in steroid hormone metabolism such as DHRS2 (p-value=3.13e-05), and AKR1B15: p-value=4.12e-05) were upregulated on Day 60.
Conclusions: A single 60 mg dose of subcutaneous denosumab injection was associated with alterations in pathways involved in hormone, immune and inflammatory signaling in the breast tissues of healthy premenopausal women with dense breasts.
Citation Format: Michael Waters, Kay Jayachandran, Debbie Bennet, Jin Zhang, Katherine Weilbaecher, Ian S. Hagemann, Graham A. Colditz, Catherine M. Appleton, Adetunji T. Toriola. Pilot phase I clinical trial of RANKL inhibition and breast tissue gene expression in high-risk premenopausal women with dense breasts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2206.