The standard therapy for thyroid cancer is surgery followed by radioactive iodine. The radioactive iodine is given in part to kill thyroid cancer cells remaining in the body after surgery. However, for some patients with higher-risk thyroid cancer, radioactive iodine alone does not completely eliminate all residual thyroid cancer cells or prevent thyroid cancer from coming back after surgery.
The goal of this study is to see if the investigational drug selumetinib (which inhibits a protein commonly involved in cancer called MEK) can improve how well radioactive iodine works against thyroid cancer and increase the chance of achieving a complete remission. Patients will be randomly assigned to receive a single dose of radioactive iodine after surgery with either selumetinib or a placebo. Selumetinib is taken orally (by mouth).