Background: \- GI-6207 is an experimental cancer vaccine made with baker's yeast. The yeast has been modified to help the immune system target a protein called CEA. CEA is found on the surface of some kinds of tumor cells, including thyroid cancer cells. Researchers want to see if GI-6207 can encourage the body's immune system to attack and kill tumor cells that contain the CEA protein. They will test to see whether this vaccine is a safe and effective treatment for medullary thyroid cancer that has not responded to earlier treatments. Objectives: \- To test the safety and effectiveness of the GI-6207 vaccine for advanced medullary thyroid cancer. Eligibility: \- Individuals at least 18 years of age who have medullary thyroid cancer that has not responded to earlier treatments. Design: * Participants will be screened with a physical exam and medical history. They will provide blood and tumor samples and have an imaging study of the neck and chest. They will also have a skin test to make sure that they are not allergic to the yeast in the vaccine. * Participants will be divided into two groups. One group will start to take GI-6207 immediately for 1 year. The second group will have 6 months of monitoring and tests with no vaccine, and then will take GI-6207 for 1 year. * GI-6207 will be given every other week for the first seven visits (about 3 months), and then monthly for the remaining year of treatment. It will be given as injections beneath the arm and in the upper thigh. These locations will help the vaccine enter the lymph nodes and reach the immune system more quickly. * Participants will be monitored with frequent blood and urine tests and imaging studies. * Participants will have regular follow-up visits after their year of study vaccines.
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Calcitonin Growth Rate
Timeframe: after 6 months of therapy