Abstract Background: Prognostically relevant biomarkers in breast cancers can be assayed using nucleic acid (e.g. OncoType DX) or protein based (e.g. immunohistochemistry (IHC)) detection stratagies. Nucleic acid tests measure many more markers compared to immunohistochemistry, but are weighted heavily for ER, PR, and HER2 in their prognostic scoring algorithms. Recent data suggest that a panel of 4 IHC stains (IHC4) may have equivalent prognostic ability to multigene assays. The aim of this study was to retrospectively compare IHC4 scores to OncoType DX recurrence scores in a large cohort of patients in our statewide health system. Methods: Formalin-fixed paraffin-embedded breast cancer samples previously submitted for OncoType DX testing between 2008 and 2011 were obtained and sections stained for ER, PR, HER2, and Ki67 (the IHC4 staining panel). Stained slides were scanned digitally and scored using customized pathologist assisted image analysis algorithms (Leica Biosystems Aperio, Vista CA). The resulting data were used in the modified “Magee Equation 3” (Klein et al. Mod Pathol. 2013. PMID: 23503643) to calculate an IHC4 recurrence score on a numerically comparable scale to that used in the OncoType score. The IHC4 and Oncotype DX scores were directly compared for concordance and correlation. Results: 280 breast cancer samples comprised the study cohort. The mean (median) IHC4 score was 20.13 (19), range: 11-42. The mean (median) OncoType score was 18.48 (16), range: 0-75. Using cut-offs of 0-17 for low risk, 18-30 for intermediate risk, and >30 for high risk, the concordance data is shown in Table 1. Comparison of scores from IHC4 and OncoType by Risk Category OncoType RS LowIntermedHigh Low80201IHC4 RSIntermed816819 High029RS = Recurrence Score Pearson's correlation coefficient for the entire set was 0.6669. The overall concordance was 56.1%; one-step discordance 43.6%; and two-step discordance: 0.3%. Eliminating the intermediate scores, the concordance was 98.8%. Conclusions: Reasonable agreement was seen between risk scores derived by IHC4 and OncoType DX. Only one discrepancy among 280 scores would have resulted in a different treatment recommendation (low risk by IHC4 and high risk by OncoType). If the IHC4 score is clearly high or low, one would not expect a dramatically different result from Oncotype DX, and the Oncotype DX test may not be needed. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-06-34.