SPHK1 and breast cancer: Because lymphatic metastasis is a major determinant for the staging and prognosis of breast cancer [200,201] and due to the importance of SphK1 in cancer progression as discussed above, we used an improved syngeneic breast cancer cell implantation method to examine the effect of SphK1 specific inhibitor, SK1-I, on tumor-induced lymphangiogenesis and cancer progression.