Abstract 2669: Solid tumor microenvironments cause more mutations than liquid or soft tumor microenvironments -- even before selection

Abstract Sequencing of many types of tumors shows that solid tumors are far more mutated than liquid tumors and soft tumors such as brain tumors, but it is unclear whether the differences are caused by induction of more mutations or subsequent selective pressures. Our pan-cancer analyses of clinical data shows increased chromosomal changes associate with collagen-I and further shows that genetic variance between patients also increases with the mean for a given tumor type. Using a 3D hydrogel-based model with tunable stiffness and of cancer spheroids, we discover that matrix stiffness increases mitotic aberrations including micronuclei and also increases chromosome loss as detected using live cell chromosome reporters (ChReporters). However, stiffness suppresses growth and size variation, which indicates more mistakes per division. Our approach is >10-fold more sensitive than sequencing approaches, and we quantify colonies of ChReporter-negative cells within cancer spheroids. Our results are consistent with Luria-Delbruck’s theory of heritable genetic changes which predicts inter-spheroid variance greatly exceeds Poisson statistics. Knockdown of myosin-II, a well-known mechanosensor, increases chromosomal loss and variance without affecting spheroid growth, consistent with a tumor suppressor role. Various drug strategies provide deeper insight into mechanisms, and use of clinically deployed CDK4/6-inhibitor reveals this drug on its own drives micronuclei formation and genetic variation. Citation Format: Dennis E. Discher, Markus Sprenger. Solid tumor microenvironments cause more mutations than liquid or soft tumor microenvironments -- even before selection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2669.