PTGER4 and neoplasm: We hypothesized that selective EP4 deletion in myeloid cells might have profound effects on tumorigenesis in ApcMin/+mice because myeloid cell EP4 receptors may mediate the actions of PGE2 generated by both COX-1 and COX-2 from myeloid cells as well as other cell types (non-myeloid stromal cells and tumor epithelial cells).