HER2 testing results, practices, and preferences among pathologists and oncologists in the US community setting: a mixed-methods study.

PURPOSE: To quantify the proportion of HER2-negative metastatic breast cancers with low or ultralow levels of HER2 expression and identify facilitators and barriers to HER2 testing and reporting in US community settings. METHODS: Analysis of electronic medical record data from a retrospective cohort of patients diagnosed with HER2-negative breast cancer from 2018 to 2023 within the Guardian Research Network, classifying HER2 status by immunohistochemistry (IHC) score. Analysis of responses to surveys of community-based pathologists and oncologists, supplemented by qualitative analysis of one-to-one interview transcripts. RESULTS: The retrospective study identified 13,824 patients diagnosed with HER2-negative breast cancer from seven healthcare organizations, with 13,100 patients included in the final cohort. Patients were classified as HER2 IHC 0 (32%), 1 + (35%), 2 + (18%), and 3 + (1%); 15% of patients did not have a documented IHC score. Surveys and interviews with 63 community-based pathologists and oncologists found that most pathologists (93%) reported discrete IHC scoring on pathology reports, but 16% had difficulty assigning scores between IHC 0 and IHC 1 + . Barriers included inadequate standards, increased interpretation time, and workflow disruptions. Digital pathology was used by 39% of pathologists, with improved accuracy, higher efficiency, and reduced subjectivity stated as advantages, and high costs and lack of practice standards as barriers to adoption. CONCLUSION: While innovative testing tools were viewed favorably by pathologists and oncologists, cost and need for training were barriers to adoption. Improving documentation practices, standardizing protocols, and adopting tools such as digital pathology could enhance the accuracy and consistency of HER2 testing.