Abstract Purpose: Most hormone receptor (HR)+/HER2− breast cancer patients respond unfavorably to neoadjuvant chemotherapy (NAC); however, genomic tests may identify those patients who are likely to benefit. Using the Prosigna assay, we first evaluated the technical performance of core needle biopsy (CNB) tissues. We then determined whether Prosigna risk of relapse (ROR) score and intrinsic subtype predicted response to NAC in HR+/HER2− patients using CNB samples. Experimental Design: Using the NanoString's nCounter Dx analysis system and a development tissue sample set, we established tissue requirements and assay output variance. We then evaluated the concordance in subtype and correlation in ROR between CNBs and corresponding surgical resection specimens (SRS) in a second independent sample set. Finally, we analyzed 180 independent CNB samples from HR+/HER2− patients who were treated with NAC and correlated ROR and intrinsic subtype with pathologic response. Results: Intra- and interbiopsy variabilities were 2.2 and 6.8 ROR units, respectively. Subtype concordance within multiple CNBs was high for the 4- and 3-subtype classifications (k = 0.885 and 0.889, respectively). Correlation in Prosigna ROR score observed between paired CNBs and SRS was high (r ≥ 0.90), and subtype concordance was also high for the 4- and 3-subtype classifications (kappa = 0.81 and 0.91, respectively). Prosigna results obtained from the HR+/HER2− patient samples showed that both ROR (P = 0.047) and intrinsic subtype (OR LumA vs. non-LumA = 0.341, P = 0.037) were significant predictors of response to NAC. Conclusions: Prosigna ROR and intrinsic subtype are readily obtained from CNB samples in normal practice and reliably predict response to NAC in HR+/HER2− patients. Clin Cancer Res; 22(3); 560–6. ©2015 AACR.