  We study the competition for space between two cell lines that differ only in
the expression of the Ras oncogene. The two cell populations are initially
separated and set to migrate antagonistically towards an in-between stripe of
free substrate. After contact, their interface moves towards the population of
normal cells. We interpret the velocity and traction force data taken before
and after contact thanks to a hydrodynamic description of collectively
migrating cohesive cell sheets. The kinematics of cells, before and after
contact, allows us to estimate the relative material parameters for both cell
lines. As predicted by the model, the transformed cell population with larger
collective stresses pushes the wild type cell population.
