The present invention relates to a method for the diagnosis or the prognosis of metastasis in prostate cancer which comprises determining if the c-MAF gene is amplified in a primary tumor sample. Likewise, the invention also relates to a method for the diagnosis or the prognosis of metastasis in prostate cancer, as well as to a method for determining the tendency to develop bone metastasis with respect to metastasis in other organs, which, comprise determining the c-MAF expression level. Finally, the invention relates to the use of a c-MAF inhibitor as therapeutic target for treating the prostate cancer.