Reliability of core needle biopsy for determining ER and HER2 status in breast cancer

Several studies have assessed the concordance of estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) status between core needle biopsy (CNB) and resection specimens, usually in small patient series and with discordant results. ER and HER2 status determined on CNB and tissue micro-arrays of resected tumors were compared for patients treated at the Leiden University Medical Center (LUMC). When results were discordant, whole-sized slides were analyzed. Additionally, literature was searched for published patient series and combined with our data to assess the concordance of ER and HER2 determination between CNB and resection specimens. In the LUMC series, concordance for ER status was 99.1%. Combined concordance from 20 studies and the LUMC patient series was 93.7%. For HER2 testing, concordance was 96.2% for patients in the LUMC series. Our study and three others have investigated the concordance when HER2 was determined according to the American Society of Clinical Oncology and College of Pathology guidelines and overall concordance was 97.8%. Concordance between CNB and surgical specimens was high for both ER and HER2 testing. However, we recommend retesting ER-negative CNB results on the surgical specimen and performing in situ hybridization assays on HER2 immunohistochemistry 3+ CNBs to confirm HER2 status.