In addition, since S1P is generated from Cer-derived sphingosine (Spn) by the action of sphingosine kinase 1 (SphK1), commonly found upregulated in BCs and related to poorer prognosis and tumor progression, changes in S1P/Cer ratio and SphK1 activity are currently the best characterized outcomes of the alterations of SL metabolism in BCs, along with their effects on chemotherapy and chemoresistance [24,25,26] and on the tumor microenvironment (TME) [26]. Here, SPHK1 is linked to neoplasm.