INTRODUCTION Cancer growth, and as a particular example in this paper, solid tumor growth, is a complicated phenomenon involving many interrelated processes across a wide range of spatial and temporal scales, and as such presents the mathematical modeler with a correspondingly complex set of problems to solve. e aim of this paper is to formulate a multiscale mathematical model of solid tumor growth, incorporating three key features: the avascular growth phase, the recruitment of new blood vessels by the tumor (angiogenesis), and the vascular growth and host tissue invasion phase.