SPHK1 and glioblastoma: Van Brocklyn et al. (2005) showed that high expression levels of the SphK isoform SphK1 in human astrocytomas correlates with a 3fold shorter median survival of patients whereas in glioblastoma cell lines, RNA interference to knock down SphK2 even had a greater effect on tumor cell proliferation than knock down of SphK1 (Van Brocklyn et al., 2005).