- FdCyd (also called 5-fluoro-2'-deoxycytidine) and THU (also called tetrahydrouridine) are experimental cancer treatment drugs. FdCyd may change how genes work in cancer cells. THU helps keep FdCyd from being broken down by the body. FdCyd and THU have been given to people on other cancer treatment trials, usually by vein. Researchers want to give FdCyd and THU by mouth to see if they work against cancers that have not responded to earlier treatments.