Abstract: The present invention provides an in vitro method for detecting tumor growth and diagnosing or prognosticating the risk of metastasis in a human subject that has been diagnosed with uveal melanoma, wherein the method comprises using, as an indicator, the levels of PMEL/ME20-S/gp 100 positive exosomes, obtained from a biological sample isolated from the human subject selected from the list consisting of blood, or serum, of at least melanocyte protein PMEL/ME20-S/gp 100, and obtaining a result of the method by comparing the levels of at least said protein with a reference value or with the levels of a control, wherein an increase of melanocyte protein PMEL/ME20-S/gp 100 is indicative of a risk of the patient having or suffering from metastasis.