On the Cover: Heterogeneity in tyrosine kinase receptor expression exists among different tumor cells, as demonstrated in KM12SM orthotopic human colon cancers grown in nude mice. Double immunofluorescence staining was performed for epidermal growth factor receptor (EGFR; green) and vascular endothelial growth factor receptor 2 (VEGFR2; red). Many tumor cells express both EGFR and VEGFR2 (yellow staining); others express only EGFR or only VEGFR2 (see page 358).