Pericyte coverage was decreased by ~32% in Hb-egf mutant angiogenic islets (Fig. 7B), by ~24% in large tumors (Fig. 7C), and by ~41% in small tumors (ø ≤ 3 mm—Fig. 7D) from Hb-egf mutant RT2 mice (representative tumor panels from each genotype, Figs. 7 E-F). The gene discussed is GSTM1; the disease is neoplasm.