Thalidomide-O-PEG-Propargyl Ester is a chemical compound that has been developed as an anti-cancer therapeutic agent. It is a new form of thalidomide, a pharmaceutical originally developed to treat morning sickness in pregnant women. The new compound is an ester of thalidomide and polyethylene glycol propargyl ether (PEG-PA), which is a chemical with the ability to bind to certain proteins in the body and decrease their activity. This could help reduce the growth of tumor cells in cancer patients.