Abstract IA012: Mammary epithelial architecture modulates field cancerization Free

The architecture of the human breast undergoes extensive remodeling throughout puberty, the menstrual cycle, pregnancy and involution with a risk of accumulating genetic alterations and tissue changes. Cells that have acquired mutations in driver genes are found to be abundant in tissues of healthy individuals, but they rarely develop into tumors. Yet, the underlying protection mechanisms that prevent tumor formation are largely unknown. Here, we utilized tissue clearing and imaged 15 normal human breasts and DCIS resections with cellular resolution to unravel the 3D architecture of thousands of mammary ducts. Surprisingly, our analysis revealed that disease-free breasts carry a high burden of microscopic tissue lesions. Distinct trees from the same breast differ in the kind and frequency of lesions, which coevolve scattered along the ductal routes. Interestingly, combining tissue clearing of FFPE archival material with spatial CNV-seq reveals that in half of the cases disease-free ductal segments neighboring DCIS lesions contain molecular alterations. To resolve the mechanisms that restrain and permit mutation spread, we compare the clonal fate behavior of cells that acquire oncogenic mutations with those bearing neutral mutations in the mouse mammary gland epithelium. From the quantitative analysis of the clonal dynamics, we find that local tissue remodeling during the estrous cycle leads to the stochastic elimination of the majority of mutant clones, while massively accelerating the expansion of a minority of clones that, by chance, survive. Thereby, oncogenic mutations can be spread along entire ducts before signs of transformation become visible. Together this data provides quantitative understanding of the earliest stages of epithelial evolution preceding disease.

Citation Format: Hendrik Messal, Colinda Scheele, Esther Lips, Catrin Lutz, Stefan Hutten, Petra Kristel, Carmen Vlahu, Jos Jonkers, Jelle Wesseling, Jacco van Rheenen. Mammary epithelial architecture modulates field cancerization [abstract]. In: Proceedings of the AACR Special Conference on Rethinking DCIS: An Opportunity for Prevention?; 2022 Sep 8-11; Philadelphia, PA. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_1): Abstract nr IA012.