“…Mathematical models, on the other hand, can be freely used to explore such ideas. There exist an abundance of mathematical models for chemotherapy under tumor heterogeneity ranging from rudimentary models that just distinguish a small number of sub-populations (e.g., Hahnfeldt et al [21], Ledzewicz and Schättler [27,29,31]) to models with increasing degrees of resistance (e.g., Swierniak et al [55,56] or Wang and Schättler [58]) and even a continuum of traits (e.g., Lorz et al [34,35], Billy and Clairambault [3], Delitalia and Lorenzi [8,10], Lavi, Green et al [19,24]). Recurrent conclusions that can be drawn from a variety of these models are that, indeed, if conditions are right (i.e., under assumptions on the relative growth rates of the sub-populations and about the effectiveness of the drugs) it is possible to limit cancer growth through a judicious choice of drug administration schedules.…”