PTGS2 and neoplasm: Previous studies had demonstrated that inhibiting COX-2 or EP4 receptor activity reduced proliferative and spheroid forming ability of COX-2 expressing murine C3L5 mammary cells in vitro22, orthotopic tumor growth and spontaneous metastases in vivo18,21,22 and the incidence of SLC marker positive cells within the residual tumors in treated mice22.