In the context of breast cancer, Nava et al. (2002) first suggested a role of SPHK1 in ER-positive breast tumorigenesis when they observed that ER-positive breast cancer cells with SPHK1 overexpression were highly tumorigenic with enhanced capability to induce larger breast tumors in mice (Nava et al., 2002). Here, SPHK1 is linked to breast carcinoma.