Proteomics is a rapidly expanding discipline that aims to gain a comprehensive understanding of the expressions, modification, interactions, and regulation of proteins in cells. New high-throughput technologies, such as protein chips and isotope-coded affinity tag peptide labeling, coupled with classic technologies such as two-dimensional gel electrophoresis and mass spectrometry, complement genomic technologies, providing cancer researchers with powerful tools for cancer diagnosis and prognosis and for the identification of targets for therapy.