Concordance of Ki-67 with 21-Gene Expression Profile (rs) in Early-Stage Breast Cancer.

e11510 Background: The RS (Oncotype DX) is widely used in the U.S. to better define risk and help clinical decision-making in breast cancer (BC). However, it is an expensive tool for underinsured patients or in low-resource settings. Ki-67 is a widely available marker for tumor proliferation and could be used to define risk. However, there have been issues with Ki-67 scoring methods and standardization. We sought to determine the clinical validity of Ki 67 in relation with RS at our institution. Methods: After IRB approval, we identified 110 consecutive patients with early stage, ER-and or PR-positive, invasive BC who were recommended RS testing as part of their clinical care (2006-2013). Ki 67 was determined by IHC [rabbit monoclonal (30-9) from Ventana (Tucson, AZ.)], and reported for the nuclear staining as the percentage of positively stained cells . We tested the performance of Ki-67 with RS (low, Intermediate, high) using various cut offs of Ki-67. Raw agreement and weighted Kappa agreement with the...