Inspired by the often staggering difference in small cytotoxic molecule-based (e.g., IFN-γ) breast cancer inhibitory effects between in vitro (nearly complete response) and in vivo (only partial response), here we focus on modeling spatial effects that are present in tissue in vivo but virtually absent in cell monolayers in vitro, specifically the diffusion of IFN-γ through tumor tissue. This evidence concerns the gene IFNG and neoplasm.