Most of the completed pre-clinical breast cancer studies investigating the inhibition of PGE2 downstream of COX-2 have focused on EP4 signaling, yet PGE2 signals through four EP receptors, and while the data thus far suggests that EP4 is the most important in terms of cancer, signaling through EP2 activates some stemness pathways. This evidence concerns the gene PTGER2 and breast carcinoma.