To evaluate signaling pathways mediating tumor endothelial Notch4 function, we conducted endothelial translatomic analysis using the Rpl22tm1.1Psam (RiboTag) system, whereby we isolated cell type–specific polysome-bound mRNA (19) in combination with endothelium-specific Cdh5TgCreERT2, referred to as RiboTagEC mice. The gene discussed is NOTCH4; the disease is neoplasm.