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The NIH defines a biomarker as "a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention."
A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease. A biomarker may be used to see how well the body responds to a treatment for a disease or condition. Also called molecular marker and signature molecule.
They are important in new diagnostic tests, and are used in screening, research and genetic studies. As more and more sensitive methods allow us to identify more biomarkers, they help create a more detailed picture about a particular disease.
There is growing interest in biomarker-driven personalized cancer therapy (precision medicine). Molecular tests, including next generation sequencing, have been developed to detect biomarkers that have the potential to predict response of cancers to particular targeted therapies. Detection of cancer-related biomarkers is only the first step in the battle, deciding what therapy options to pursue can be more difficult, especially when tumors have more than one potentially actionable aberration. Further, different mutations/variants in a single gene may have different functional consequences, and response to targeted agents may be context dependent.
Early clinical trials with new molecular entities are increasingly conducted in a biomarker-selected fashion, and even when trials are not biomarker-selected, much effort is placed on enrolling patients onto clinical trials where they have the highest probability of response.
The development of trastuzumab for human epidermal growth factor 2 (HER2)-positive breast cancer dramatically altered the outcome of patients with HER2-positive disease, providing a prime example for the success of biomarker-driven, personalized cancer therapy. Objective response rates for first-line trastuzumab treatment in patients with and without HER2 gene amplification by fluorescence in situ hybridization (FISH) analysis were 34% and 7%, respectively (Vogel et al., 2002), illustrating the efficacy of targeted therapies in tumors harboring molecular aberrations predicted to mediate therapy sensitivity.
Over a dozen targeted therapies have been approved with companion diagnostic tests, assays that predict tumor response to therapy, aimed at assisting in the decision of which targeted therapy strategies should be utilized for specific patients. These include assessment of BRAF V600 mutations for administration of anti-RAF and anti-MEK therapies in melanoma and BCR-ABL gene fusions for the use of imatinib in treating chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL).