Uveal Melanoma, Posterior, Medium/Large Size

Uveal melanoma (UM) is the most common type of cancer inside the eyes of adults. Almost half of all patients diagnosed with UM will eventually develop metastases. Once metastases occur, the median patient survival is short. In this trial, we will test if treatment with Melatonin after primary tumor diagnosis can prevent or delay the development of metastases. 100 patients diagnosed with primary UM will be randomized to either treatment with Melatonin tablets (20 mg at night), or to a control group. Both groups will be followed for 5 years. At 5 years, the number of patients that have developed metastases in the Melatonin and control groups will be compared (primary outcome measure).