A method for determining whether a mammalian subject having a malignant melanoma belongs to a first or a second group, wherein the prognosis of subjects of the first group is better than the prognosis of subjects of the second group is provided. The method comprises the steps of: evaluating an amount of RBM3 protein in at least part of a sample earlier obtained from the subject and determining a sample value corresponding to the evaluated amount； comparing said sample value with a predetermined reference value； and if said sample value is higher than said reference value, concluding that the subject belongs to the first group； and if said sample value is lower than or equal to said reference value, concluding that the subject belongs to the second group.
