Biomarker

Biomarker is a substance used as an indicator of a biologic state

Description
It may mean the following:
 * 1) It can be any kind of molecule indicating the existence (past or present) of living organisms. In particular, in the fields of geology and astrobiology biomarkers are also known as biosignatures. The term is also used to describe biological involvement in the generation of petroleum (see Biomarker (petroleum)).
 * 2) In medicine, a biomarker can be a substance that is introduced in an organism as a means to examine organ function or other aspects of health. For example, a radioactive Iodine isotope to evaluate the function of the thyroid gland.
 * 3) In medicine, a biomarker can be a substance whose detection indicates a particular condition or disease state (for example, the presence of antibodies against a virus named CMV may indicate a past or present infection by CMV). More specifically, a ""biomarker"" indicates a change in expression or state of a protein that correlates with the risk or progression of a disease, or with the susceptibility of the disease to a given treatment. Once a proposed biomarker has been validated, it can be used to diagnose disease risk, presence of disease in an individual, or to tailor treatments for the disease in an individual (choices of drug treatment or administration regimes). In evaluating potential drug therapies, a biomarker may be used as a surrogate for a natural endpoint such as survival or irreversible morbidity. If a treatment alters the biomarker, which has a direct connection to improved health, the biomarker serves as a ""surrogate endpoint"" for evaluating clinical benefit.
 * 4) In cell biology, a biomarker is a molecule that allows for the detection and isolation of a particular cell type (for example, the protein Oct-4 is used as a biomarker to identify embryonic stem cells).
 * 5) A biomarker can also be used to indicate exposure to various environmental substances in epidemiology and toxicology. In these cases, the biomarker may be the external substance itself (e.g. asbestos particles or NNK from tobacco), or a variant of the external substance processed by the body (a metabolite). (See Bioindicator)
 * 6) In genetics, a biomarker (identified as genetic marker) is a fragment of DNA sequence that causes disease or is associated with susceptibility to disease