Prof. Dr. Josef A. Käs

Universität Leipzig

As early as 50 AD, the Roman medical encyclopaedist Celsus recognized that solid tumours are stiffer than surrounding tissue.  However, cancer cell lines are softer, which facilitates invasion.  This paradox raises several questions:  Does softness emerge from adaptation to mechanical and chemical cues in the external microenvironment, or are soft cells already present inside a primary tumour?  If the latter, how can cancer tissue be more rigid than normal tissue and yet contain more soft cells?  Here we show that in primary samples from patients with mammary and cervical carcinomas, cells do exhibit a broad distribution of rigidities, with a higher fraction of softer and more contractile cells compared to normal tissue.  Mechanical modelling based on patient data reveals that tumours with a significant fraction of very soft cells can still remain solid.  Moreover, in tissues with the observed distributions of cell stiffness, softer cells spontaneously self-organize into multicellular streams, possibly facilitating cancer metastasis.