Biomarkers are biological indicators of early disease detection (diagnostic), disease progression and outcome (prognostic), and response to therapy (predictive). The inclusion of biomarkers in patient selection has led to superior drug response rates and increased overall survival in pivotal clinical trials. Also, use of biomarkers to select drug sensitive patients have greatly improved the quality of life by improving therapeutic efficacy and reducing toxicity. Biomarkers discovered and used in clinical trials have been approved as companion diagnostics and used routinely in making treatment decisions.