Identifying patients at risk of relapse while undergoing particular treatment protocols is critically important yet challenging to do in a timely manner. Researchers at Washington University have deveoped a new method to rapidly and accurately determine relapse risk in a human subject afflicted with estrogen receptor-positive breast cancer treated with adjuvant endocrine monotherapy. This method involves a proprietary scoring system to analyze gene expression profiles of breast tissue samples. The method has been validated in multiple independent public micro-array data sets and patient cohorts.