PTGER4 and neoplasm: PGE2 acting via G-protein coupled rhodopsin-type prostanoid receptors E 1–4 (EP1, EP2, EP3, EP4) triggers various tumor-associated intracellular signaling pathways, out of which the most remarkable ones are the stimulation of the epidermal growth factor-receptor (EGFR), the phosphorylation of protein kinase C (PKC)-mediated extracellular signal-regulated kinase (ERK), and the activation of G-protein dependent beta-catenin [1,2,12,16,17].