Biochemical markers in oncology are molecules that can be detected in higher or lower than normal amounts in the blood, urine, or body tissues of some people with certain types of cancer. A tumor marker may be produced by the tumor itself, by the surrounding normal tissue in response to the presence of tumor or by the tissue of metastases. Biomarkers may be able to define risks and identify the early stages of tumor development, assist in tumor detection and diagnosis, verify stratification of patients for treatment, predict outcomes of the disease, and help in surveillance for disease recurrence.