Macrophage inhibitory cytokine-1 (MIC-1) is a member of the transforming growth factor-ß superfamily that regulates a wide variety of physiological processes involved in tissue differentiation and maintenance. MIC-1 is synthesized as a 62-kDa intracellular protein, which, after cleavage by a furin-like protease, is secreted as a 25-kDa disulfide-linked dimeric protein. Expression of MIC-1 results in inhibition of macrophage activation, regulated by the p53 pathway, in response to pro-inflammatory monokines. MIC-1 is involved in tumor pathogenesis and its measurement can be used as a clinical tool for the diagnosis of a wide range of cancers. It could be a useful marker for aggressive prostate cancer while MIC-1 is upregulated in advanced and more aggressive prostatic tumors.