In prostate cancer, S1P proved to be correlated with prostate-specific antigen (PSA) and lympho node status and the same authors hypothesized that S1P and Sphk1 transported inside red blood cells, the major biological source of blood S1P, may be considered reliable biomarkers for the early detection of prostate cancer [29]. The gene discussed is KLK3; the disease is prostate carcinoma.