Imaging Study for FdCyd and THU Cancer Treatment

Background: \- The drugs FdCyd (also called 5-fluoro-2'-deoxycytidine) and THU (also called tetrahydrouridine) are being used in a cancer treatment study. Not a lot is known about how FdCyd works in the body. Researchers want to look at a modified form of FdCyd using imaging studies to see how the drug reacts with the cancer. This study is not a treatment study. It is open only to people who are already on the FdCyd and THU cancer treatment study. Objectives: \- To study how FdCyd affects advanced cancer cells. Eligibility: \- Participants in National Cancer Institute study 09-C-0214. Design: * Participants will have two imaging studies, one before starting FdCyd and THU treatment and one after starting treatment. * Participants will have the modified FdCyd, known as F-18 FdCyd, with a dose of THU. The doses will be followed by two imaging study scans and frequent blood samples. * This procedure will be repeated at a later date, during the FdCyd and THU treatment period. * Treatment will not be provided as part of this study. This is an imaging study protocol only....