Not Just Soft: Cell Viscosity Emerges as a Driver of Tumor Cell Dissemination

The mechanical properties of cells and tissues have emerged as important biophysical markers for distinguishing between healthy and diseased states. In cancer, mechanical heterogeneity spans multiple scales, from tissue-level variations to substantial differences between individual tumor cells. The prevailing notion is that metastatic cancer cells are typically elastically softer than their non-malignant counterparts, a feature attributed to their ability to deform, remodel their shape, and navigate dense extracellular matrices and constricting blood vessels. However, cells are not purely elastic materials, but instead they exhibit viscoelastic behavior, in which deformation depends not only on instantaneous stiffness but also on time-dependent internal flow. In this context, Gensbittel and colleagues find that cellular viscosity, rather than elasticity, is a key determinant of cancer cell dissemination and extravasation, providing new insights into the mechanical underpinnings of cancer metastasis.