SPHK1 and colorectal cancer: In the first report, PF-543 did not exert strong inhibitory effects at low concentration on 1483 cells.13 However, after incubation for 4 days at a concentration of 10 μM, significant inhibition of proliferation of colorectal cancer cells was reported.19 As PF-543 inhibits the activity of SphK1 and reduces the level of S1P, which is essential for suppressing cell proliferation, long-term treatment may be necessary to exert anti-proliferative effects.