ABSTRACT
A tumor marker is defined as a molecule or substance produced by or in response to neoplastic proliferation, which enters the circulation in detectable amounts. It indicates the likely presence of cancer or provides information about its behavior. Since the description of Bence-Jones proteins well over a century ago, a variety of substances have been investigated as potential tumor markers, and advances in molecular biology and technology continually add to this list. Tumor markers can be broadly classified into tumor-specific antigens and tumor-associated antigens. Two examples of strictly tumor-specific antigens are the idiotypes of immunoglobulins of B cell tumors and certain neo-antigens of virus-induced tumors. The vast majority of tumor markers are in reality tumor-associated antigens. In many cases, they are initially described as highly tumor-specific, with subsequent studies uncovering their presence in multiple cancers and in normal adult or fetal tissues.
