SPHK2 and breast cancer: However, it was subsequently shown that downregulation of SphK2 inhibits the proliferation and migration of tumor cells, such as glioblastoma and breast cancer cells [17], [18] and ablation of SphK2 or employing a SphK2 inhibitor has been shown to inhibit the xenograft growth of tumor cells in mice [15], [19], [20].