Tissue tension fosters macrophage-driven lipid peroxidation-induced DNA damage.

Inflammation can induce mutagenic DNA damage to enhance cancer risk and progression. Inflammation also increases fibrosis and stromal stiffening that promotes malignancy, and tissues with higher cancer risk are often stiffer. Despite this connection, how stromal stiffness contributes to inflammatory-mediated DNA damage in tumorigenesis remains unclear. Here, we show that tissue tension engages macrophages to generate lipid peroxidation-induced DNA damage, contributing to mutational burden that may promote malignant progression. We identify that fibrotic breast tumors display higher mutational burdens. Mechanistically, tissue tension increases epithelial STAT3 to drive chemokine-mediated macrophage recruitment. Stiffness promotes reactive oxygen species-induced lipid peroxidation in recruited macrophages, generating aldehydes that damage DNA and enhance progression. Notably, high mammographically dense breast tissues-associated with increased cancer risk-are stiffer and inflamed and display elevated lipid aldehydes and DNA damage. This work links fibrosis and inflammation to tension-mediated cancer initiation and progression.