Mutations in RAS are key oncogenic drivers and therapeutic targets. Oncogenic Ras proteins activate a network of downstream signalling pathways, including extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K), promoting cell proliferation and survival. However, there is increasing evidence that RAS oncogenes also alter the mechanical properties of both individual malignant cells and transformed tissues. Here we discuss the role of oncogenic RAS in controlling

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... nical cell phenotypes and how these mechanical changes promote oncogenic transformation in single cells and tissues. RAS activation alters actin organisation and actomyosin contractility. These changes alter cell rheology and impact mechanosensing through changes in substrate adhesion and YAP/TAZ-dependent mechanotransduction. We then discuss how these changes play out in cell collectives and epithelial tissues by driving large-scale tissue deformations and the expansion of malignant cells. Uncovering how RAS oncogenes alter cell mechanics will lead to a better understanding of the morphogenetic processes that underlie tumour formation in RAS-mutant cancers.