SPP1 and breast carcinoma: At the time our adjuvant studies were started, OPN as a potential tumor biomarker in breast cancer was categorized as “+” on the Tumor Marker Utility Grading System (TMUGS) published by Hayes et al. [4], defined as “sufficient data are available to demonstrate that the marker correlates with the biologic process and/or biologic endpoint related to the use and that the marker results might affect favorable clinical outcome for that use”.