CHKA and neoplasm: When it comes to phospholipid metabolism, the extracellular choline and ethanolamine are transported into tumor cells to be catalyzed by a series of enzymes such as ethanolamine kinase (ETNK), choline kinase (ChK), cytidylyltransferase (CT), diacylglycerol phosphotransferase (PT), and respectively converted into phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEth) (69, 70).