Cholesterol ester transfer protein: A protein that helps regulate the size of cholesterol particles and influence the process of atherogenesis (the formation of plaques in arteries). Abbreviated CETP. The CETP gene is in chromosome band 16q21. A number of mutations are known in the CETP gene. Some result in CEPT deficiency, increased levels of HDL ("good") cholesterol and unusually large cholesterol particles. CETP deficiency appears to be a good mutation which is antiatherogenic and may confer unusual longevity to the person. Also called cholesteryl ester transfer protein.