PTGER4 and breast cancer: We found in multiple studies that EP4 on breast cancer cells accounts for numerous COX-2 mediated mechanisms in breast cancer progression: increased migration and invasion [22–24], VEGF-C/D upregulation [26, 27] promotion of tumor-associated angiogenesis and lymphangiogenesis in vivo [27] and finally, induction of stem-like cells [37, 38].