Evolutionary game theory has been used to model cancer for more than a decade. Efforts to date have focused on understanding the effect of interactions between cancer cells of different types, and between aspects of the tumour microenvironment and cancer cells. To realise the full potential of these modelling efforts however, we submit that a method for direct parameterisation is required. In this talk, I will present our novel ‘evolutionary game assay’ designed specifically to parameterise a two strategy matrix evolutionary game from in vitro experiments comprised of co-culture of cells transfected with different colour fluorescent proteins. I will also show the results of the first game we measured, a game between EML4-ALK translocated non-small cell lung cancer cells before and after we evolved resistance to Alectinib (a targeted therapy). We find that these cells play either the Leader or Deadlock game, depending on different therapeutic and microenvironmental conditions. This change in game, as modulated by treatment, also suggests a novel therapeutic strategy which we have posited before is possible: treating the game instead of the player.