“…Introduction. During the past few decades, an increasing number of mathematical models describing tumor growth with a free boundary have been studied and developed in many papers; see [1,2,3,4,5,7,8,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51] and the references therein. These models usually contain one or more reaction-diffusion equations describing the concentration of substrates such as nutrients and inhibitors, and one or several first-order nonlinear partial differential equations describing the evolution and mov...…”