Abstract: The present invention relates to a method of discovering pharmacogenomic biomarkers that are correlated with varied individual responses (efficacy, adverse effect, and other end points) to therapeutic agents. The present invention provides a mean to utilize archived clinical samples to perform genome-wide association study in order to identify novel pharmacogenomic biomarkers. The newly discovered biomarkers can then be developed into companion diagnostic tests which can help to predict drug responses and apply drugs only to those who will be benefited, or exclude those who might have adverse effects, by the treatment.