| Abstract: |
Recent studies since the 2018 ASCO/CAP guideline update for HER2 testing in breast cancer have made novel discoveries in HER2-targeted therapy. These studies have elucidated a new subtype of breast cancer known as “HER2-low” breast cancers, which represents a distinct subgroup under what has been classified as HER2-negative breast cancer. Additionally, there is further understanding of alterations within the ERBB2 gene, including mutations in the tyrosine kinase domain, both de novo or as a resistance mechanism. Finally, better understanding of the HER2 immunohistochemistry (IHC) patterns in specific histologic subtypes of breast cancer, such as invasive micropapillary breast carcinoma, has allowed for more accurate classification of HER2 IHC. All of these findings have important implications for HER2-targeted therapy and overall outcomes. © 2022 |
