Researchers at INSERM have identified cellular viscosity as a critical biophysical parameter controlling cancer metastasis. Cancer cells with reduced internal viscosity demonstrate enhanced ability to deform, squeeze through tight spaces, and migrate to distant organs. The team discovered that metastatic cells exhibit significantly lower cytoplasmic viscosity compared to primary tumor cells, allowing them to navigate the complex mechanical barriers of blood vessels and tissue matrices more efficiently. This viscosity reduction appears linked to altered protein expression patterns and cytoskeletal reorganization within migrating cancer cells. The finding represents a paradigm shift in understanding metastatic mechanics, moving beyond traditional genetic and molecular markers to include fundamental cellular physics. For oncology practice, measuring cellular viscosity could provide a novel biomarker for metastatic potential, potentially identifying high-risk patients earlier than current methods. The research also suggests therapeutic targets focused on increasing cancer cell viscosity to mechanically trap cells and prevent dissemination. However, the challenge lies in selectively targeting cancer cell viscosity without affecting normal cell function. This biophysical approach could complement existing treatments by addressing the mechanical aspects of metastasis that have been largely overlooked in favor of biochemical interventions.