Even though the presence of cancer-associated fibroblasts (CAFs) in the vicinity of tumors is well documented, it is not clear whether they promote or inhibit the escape and migration of the cancer cells away from the primary tumor. In vivo experiments monitoring the morphology of tumors in mice are very valuable, but are too complex to infer a physical mechanism. Here, we propose an interdisciplinary experimental program that aims at investigating the processes involved in cocultures of CAFs and tumor cells (TCs). Experiments will initially be performed on Ewing tumor cells, an aggressive cancer targeting teenagers and young adults. In a second step, breast cancer cells will also be studied. Sorting of the CAFs and TCs is dictated not only by the cell/cell adhesive properties and rheology, as would be the case for passive materials, but also by the CAFs’ “nematic” organization (their propensity to align along a common direction) and their active contractility, both properties potentially affecting the tumor’s structure. In close collaboration with our biology collaborators, we will use well-controlled cell lines on micro structured surfaces. The observations will be interpreted with physical theories encompassing adhesion and active nematicity. These well-controlled in vitro experiments may bring new insights into the mechanisms directing the evolution of these cancer systems in their in-vivo native environment.