A biomarker is a characteristic that is objectively measured and evaluated as an 
indicator of normal biologic processes, pathogenic processes, or pharmacologic 
responses to a therapeutic intervention. In cancer, a biomarker refers to a 
substance or process that is indicative of the presence of cancer in the body. A 
biomarker might be either a molecule secreted by a tumor or it can be a specific 
response of the body to the presence of cancer. Genetic, epigenetic, proteomic, 
glycomic, and imaging biomarkers can be used for cancer diagnosis, prognosis and 
epidemiology. These markers can be assayed in non-invasively collected 
biofluids. However, few cancer biomarkers are highly sensitive and specific for 
cancer detection at the present time. Consequently, biomarkers are not yet ready 
for routine use due to challenges in their clinical validation for early disease 
detection, diagnosis and monitoring to improve long-term survival of patients.