SPHK1 and breast cancer: We have demonstrated that S1P production is upregulated in various cancer types, including breast cancer, and that it contributes to lymphatic metastasis, and is associated with prognosis based on the histological evaluation of phosphorylation of sphingosine kinase type 1 (SphK1), the S1P-producing enzyme [61,62,63,64,65,66,67,68,69].