This is a simulation of tumour cord growth , where cells suffer from hypoxia (energy deficit shown with colour). The tumour grows along the blood vessel (coincides with x -axis). Red line shows the position of the tumour–host interface. This particular simulation was programmed in FreeFEM++ out of curiousity. The source code for simulation may be found at http://code.google.com/p/cord . This video reflects work in progress and may be different from the final results .