  In this contribution, the non-local, integro-partial differential system of
equations proposed by Hillen et al. (Bull. Math. Biol. 75, 2013, no.1, 161-184)
to account for the the tumor growth paradox (or the observation that some
incomplete cancer treatments may enhance tumor growth) is reviewed. It is shown
that when cancer cells' diffusion effects and Neumann boundary conditions are
taken into consideration, the same paradoxical tumor growth emerges.
