Phase I Trial of 4'-Thio-2'-Deoxycytidine (TdCyd) in Patients With Advanced Solid Tumors

Background: \- Genes are made up of DNA and are the instruction book for cells. When people have cancer, some of the genes that might have slowed the growth of tumor cells were turned off. Researchers think a drug called TdCyd might help to turn these genes back on. This may slow the growth of tumors in people with cancer. Objectives: \- To test the safety of TdCyd and to find out how it works. Also, to find out the dose of the drug that can be safely given to humans. Eligibility: \- Adults 18 years and older who have advanced cancer that has progressed after standard treatment, or for which no effective therapy exists. Design: * Participants will take TdCyd by mouth. The drug is given in 21-day cycles. TdCyd is taken once a day during week 1 for 5 days. Then for 2 days participants do not take the drug. Then they take it for 5 days during week 2. No TdCyd is taken during week 3. * Participants will keep a diary of their study drug doses. * Participants will have tests about every 3 weeks to see how the study drugs are affecting their body. They will have blood and urine tests, a medical history, and physical exams. They may have computed tomography (CT) scans to measure their tumors. They may have an electrocardiogram, which measures the heart electrical activity. * If participants develop any side effects, they may be asked to visit more often. * Participants will stay in the study as long as they are tolerating TdCyd and their tumors are either stable or getting better. One month after stopping the drug, they will have a follow-up phone call.