Abstract P6-05-03: Exploring the microRNA landscape of nipple aspirate fluid in the context of mammographic breast density

Background High mammographic density is an established risk factor for breast cancer but studies are needed to elucidate the etiological pathways underlying this relationship. The identification of factors (indirectly) regulating the accumulation of fat and connective tissue may help explain why high mammographic density is linked to breast cancer risk. Those factors may provide markers for predicting and even clues for modifying this risk. MicroRNAs could regulate specific cellular processes involved in regulating mammographic density, like fat accumulation, connective tissue density and immune response. Nipple aspirate fluid represents an excellent opportunity for biomarker detection within the breast microenvironment. Materials and Methods MicroRNA expression profiling was performed using TaqMan OpenArray Human MicroRNA Plates (ThermoFisher Scientific) in 40 pooled (paired left and right breast) nipple aspirate fluid samples obtained from age-matched women participating in a population-based breast cancer screening program with 9extremely dense9 (n=20) and 9almost entirely fatty9 breasts (n=20), without further abnormalities on mammography. Breast density was assessed using Volpara software in categories comparable to American College of Radiology (ACR) breast density categories. Results 25 significantly differentially expressed microRNAs were identified, including hsa-miR-19a-3p (p=0.001; upregulated in 9extremely dense9 versus 9almost entirely fatty9), hsa-miR-324-5p (p=0.003; upregulated), hsa-miR-425-5p (p=0.001; upregulated), hsa-miR-660-5p (p=0.004; upregulated), hsa-miR-29b-3p (p=0.011; upregulated) and hsa-miR-187-3p (p=0.024; downregulated). Based on expression profiles of the 8 most significantly dysregulated microRNAs alone, nipple aspirate fluid samples could reliably be classified into 9extremely dense9 and 9almost entirely fatty9 mammographic density groups (31/40 (78%) samples correctly classified). Several of the dysregulated microRNAs have been associated with regulation of collagen deposition or crosslinking (e.g. miR-29, miR-222 and let-7) and adipocyte differentiation and proliferation (e.g. miR-29, miR-222, miR-155 and let-7), suggesting that these aberrant miRNAs may play a role in the development of breast tissue with high mammographic density. In addition, pathway enrichment analysis demonstrated an enrichment of the 9proteoglycans in cancer9 pathway suggesting that proteoglycan dysregulation is intimately linked to microRNA dysregulation. Conclusions In summary, microRNA profiling has resulted in a panel of microRNAs that might help explain why high mammographic density is linked to breast cancer risk and may ultimately result in a biomarker panel for predicting this risk, or provide attractive targets for future breast cancer preventive strategies. Further validation in an independent set of nipple aspirate fluid samples from 9extremely dense9 and 9almost entirely fatty9 categories is currently ongoing. Citation Format: Moelans CB, Patuleia SI, Bakker MF, van der Wall E, van Diest PJ, van Gils CH. Exploring the microRNA landscape of nipple aspirate fluid in the context of mammographic breast density [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 P6-05-03.