Abstract 2023: Spatial transcriptomic evidence for an inflammatory, pro tumorigenic microenvironment in normal human dense breast tissue

Abstract Breast cancer affects over 2,000,000 women worldwide, with more than 680,000 deaths per year. Increased breast density is one of the risk factors for breast cancer, albeit less than the risk associated with increased age and genetic mutation. It has been suggested that high breast density accounts for 15% of the breast cancers diagnosed. On radiographic examination, breast density appears as opaque regions associated with increased cellularity and matrix, which in some circumstances contribute to difficulty observing small tumors. Dense regions in the breast have been associated with both morphological changes as well as molecular changes in the tissue. How these changes may play a role in increased risk for tumorigenesis are not well described. In this study, we examine the partial spatial transcriptomes of specific regions in normal breast tissue containing dense regions, including regions of normal density, the interface of dense and non-dense regions and the dense regions themselves using the GeoMx Digital Spatial Profiling system (DSP). Multi-label immunofluorescence was used to distinguish tissue morphology in FFPE samples from two health patients. We selected 24 regions of interest (ROIs) from each tissue section included dense, interface and non-dense breast. Using barcoded DNA oligos attached in situ hybridization probes (for RNA) via ultraviolet (UV)- photocleavable linkers, we screened over 1800 genes from Cancer Transcriptome Atlas panel. Our results indicated an elevated expression of CD68 and CD33, markers for macrophages and myeloid-derived suppressor cells (MDSCs) in dense breast regions as compared to the non-dense areas. Identifying markers for myeloid lineage cells was followed by an increased expression of the genes EOMES, TIGIT and RORA, which are engaged in the immunosuppressive phenotype. This could be hypothesized to support a pro-tumorigenesis microenvironment preventing T cells from recognizing newly arisen tumor cells. In addition, we also observed a significant expression of cytokines (IL12A and IL26) and chemokines (CCL19 and CXCL10) in the dense breast, which are involved in the regulation of inflammatory response and chemotaxis of monocytes and T-lymphocytes cells. Both CCL19 and IL26 have been demonstrated to play a role in cell proliferation. Thus, these initial studies suggest that the dense breast microenvironment is potentially a pro-tumorigenic environment that, with sufficient factors, gives rise to tumorigenesis. These data also suggest potential nodes of therapeutic intervention that may lower such risk. Citation Format: Ana Karina de Oliveira, Patcharin Pramoonjago, Christopher A. Moskaluk, Jay W. Fox. Spatial transcriptomic evidence for an inflammatory, pro tumorigenic microenvironment in normal human dense breast tissue [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 2023.