FTY720 has been demonstrated as a competitive inhibitor (with sphingosine) of SPHK1 with a Kic of 2 μmol/L[107,108] and destabilizes SPHK1 by facilitating SPHK1 degradation via ubiquitination in human pulmonary artery smooth muscle, breast cancer, and androgen-independent prostate cancer cells[108,109]. This evidence concerns the gene SPHK1 and breast cancer.