Ropidoxuridine is a thymidine analogue and an oral prodrug of iododeoxyuridine that is easier to administer and less toxic with a more favorable therapeutic index in preclinical studies. Iododeoxyuridine demonstrated a survival advantage in Phase II studies in anaplastic astrocytoma, a type of brain tumor. Ropidoxuridine may help radiation therapy work better by making tumor cells more sensitive to the radiation therapy. In 2019, phase I clinical trials were ongoing to study the best dose of ropidoxuridine and its side effects in patients with metastatic malignant neoplasm in the brain and in patients with metastatic gastrointestinal cancer. First results showed that ropidoxuridine, combined with radiation therapy, was well-tolerated in patients with metastatic gastrointestinal cancer.