“…Continuum and solid-mechanics models (Chaplain and Sleeman, 1993; Tracqui, 1995; Khain and Sander, 2006; Macklin and Lowengrub, 2007; Frieboes et al , 2007; Li et al , 2007; Swanson et al , 2003) consider physical pressures and forces among cells and TM, capturing tumor structure at the tissue level, but do not describe a tumor's cellular and subcellular properties, making mechanisms such as cell-cell adhesion difficult to include. Point-cell models ( cellular automata ) allow more realistic stochastic descriptions at cellular (Kimmel and Axelrod, 1991; Smolle and Stettner, 1993; Qi et al , 1993; Kansal et al , 2000; Dormann and Deutsch, 2002) and subcellular levels (Düchting, 1990; Düchting et al , 1996) but neglect the shapes of cells. Hybrid multi-cell models combine discrete representations of individual tumor cells with continuum representations of diffusible chemicals (Anderson, 2005; Rejniak, 2005) and either discrete, continuum or hybrid models of the surrounding tissue.…”