Protein S1-P, also known as Protein S1-E, S1 calcium-binding protein P, S1P and S1E, is a nucleus and cytoplasm protein which belongs to theS-1 family. S1P / S1E contains twoEF-hand domains. S1P protein regulates calcium signal transduction and mediates cytoskeletal interaction, protein phosphorylation and transcriptional control. S1P / S1E overexpression can upregulate androgen receptor expression and thereby promote prostate cancer progression by increasing cell growth. S1P / S1E may directly confer resistance to chemotherapy. S1P / S1E induction may be considered an important step in the initial stage of lung adenocarcinomas, whereas its downregulation in advanced stages seems to be important for tumour progression in which DNA methylation and/or feedback transcription processes play a critical role. S1P / S1E plays a major role in the aggressiveness of pancreatic cancer that is likely mediated by its ability to activate RAGE. Interference with S1P / S1E may provide a novel approach for treatment of pancreatic cancer. S1P / S1E could be considered a potential drug target or a chemosensitization target, and could also serve as a biomarker for aggressive, hormone-refractory and metastatic prostate cancer.