AFP and cancer: However, recent studies show that (i) up-regulated ceramides and sphingosine, not S1P, correlate significantly with alpha fetoprotein in serum of HCC patients and (ii) highly potent and selective SphK1 inhibitors may not affect cancer cell proliferation or survival [14, 34], thus supporting the concept that regulation through sphingosine itself might play a more important role in oncogenic transformation.