Using the COX-2 expressing murine C3L5 breast cancer model, we found that an EP4 antagonist at nontoxic doses abrogated tumor growth, tumor associated angiogenesis and lymphangiogenesis, and metastasis to the lymph nodes and the lungs, and an abrogation of stem-like cell functions in vitro and in vivo [25, 27]. Here, PTGS2 is linked to breast cancer.