Biomarkers can be classified into two major groups, disease-related and drug-related biomarkers. Disease-related biomarkers are very helpful for clinical stratification, identification of patients within the general population, disease staging, and evaluation of the likely outcome of disease. In contrast,drug-related biomarkers are biological or clinical characteristics that provide valuable information on prognosis and survival after therapeutic intervention. Such predictive factors can be employed to identify subgroups of patients who are most likely to respond to a given treatment, to create a treatment plan, and to assess the efficacy, adverse reactions, and complications of therapy. An ideal biomarker should be easily, specifically, stably, and inexpensively measured in a noninvasive or minimally invasive way with high analytical specificity and sensitivity.