Abstract 782: Correlation between collagen peptides and physical features of fibrosis in breast tissue from women at increased risk of cancer

Abstract Breast cancer risk increases significantly in women who maintain higher radiologically dense breast tissue as they age. However, the mechanisms that underlie this association remain poorly understood, especially in postmenopausal women. A predominant contributor to dense breasts and differences between women is the relative amount of fibrillar collagens. Experimental models suggest that changes in collagen properties such as fiber alignment and stiffness promote local stromal fibrosis, which we hypothesize may contribute to the relationship between breast density, aging, and tumorigenesis. Normal breast biopsy samples from the contralateral, healthy breast of 32 postmenopausal breast cancer patients participating in a clinical trial for drug effect on breast density were examined and scored for areas of fibrosis and analyzed using second harmonic generation microscopy (SHG) and mass spectrometry proteomics. Our aim was to identify areas of fibrosis and relate the severity of focal fibrosis to the physical properties and peptide composition of collagen fibers. Using GraphPad Prism, we conducted one-way ANOVA and Kruskal-Wallis tests and post-hoc multiple comparison tests. H&E-stained breast tissue samples were scored according to percent fibrosis. The minimum and maximum percent fibrosis were 5% and 100%, respectively, with a median of 60% (95% CI: 97.06%). Out of 31 people, 16 had a higher fibrosis score than the median. Consistent with pathologic scoring of the presence and extent of fibrosis, fiber counts were significantly lower in tissue with lower fibrosis scores than samples with more highly scored fibrosis (p-value <0.001). Distance to the nearest fiber was greater in samples with < 20% fibrosis, whereas greater alignment to the nearest fiber was observed in higher fibrosis percentages. At the molecular level, 22 peptides demonstrated a strong correlation with percent fibrosis (spearman r ≥ 60), of which 13 peptides were statistically significant (p-value <0.0001). The putatively identified peptides belong to type I, III, IV and VI collagens. Fiber length and straightness, but not fiber width, were higher in tissues with greater percent fibrosis. Significant correlations were identified between collagen physical features and peptides: two distinct peptides correlated with collagen fiber length and straightness while 20 peptides correlated with fiber width. These putative peptides belong to types I, III, IV and V collagens with ~70% of the peptides containing at least one hydroxyproline modification. This study is the first to explore the link between focal fibrosis and collagen-associated peptides in healthy breast tissue of high-risk postmenopausal women. These findings provide novel insights on stromal collagens associated with fibrotic changes in normal at-risk breast tissue that may act in tissue susceptibility to tumor formation. Citation Format: Denys Rujchanarong, Alison T. Stopeck, Christina Preece, Ren Sun, Pavani Chalasani, Sean Brown, Ji D. Bai, Heather Jensen Smith, Sungyong You, Peggi M. Angel, Patricia Thompson. Correlation between collagen peptides and physical features of fibrosis in breast tissue from women at increased risk of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 782.