Breast cancer progression tissue microarrays were probed with anti-Plg-RKT mAB and we found that Plg-RKT is widely expressed in human breast tumors, that its expression is increased in tumors that have spread to draining lymph nodes and distant organs, and that Plg-RKT expression is most pronounced in hormone receptor (HR)-positive tumors. Here, PLG is linked to breast neoplasm.