[Tumor markers in cancer of the digestive system]

The first tumor marker (TM) described in Oncology was the Bence-Jones protein in 1847 in patients with multiple myeloma. However, it was not until the early 60s that the first useful TM in gastrointestinal (GI) cancer was recognized, alpha fetoprotein. The development of TM has achieved enormous progress over the last years and its definition includes not only tumor products but elements inherent to the tumor such as oncogenes. A review is presented of the most important TM in GI tumors according to anatomic location. Emphasis is made in colon cancer and the clinical usefulness of carcinoembryonic antigen throughout the different stages in the management of such patients.