The Norton-Simon hypothesis and the onset of non-genetic resistance to chemotherapy induced by stochastic fluctuations

► Tumor evolution under therapy is considered. ► Under Norton-Simon hypothesis the system may be bistable. ► Bounded noise nonlinearly affects tumor carrying capacity and drug pharmacodynamics. ► Fluctuations may cause the transition from a small equilibrium to a larger one. ► A new and non-genetic kind of resistance to chemotherapy.