Evaluation of HER2/neu status by immunohistochemistry using computer-based image analysis and correlation with gene amplification by fluorescence in situ hybridization assay: A 10-year experience and impact of test standardization on concordance rate

Context.- The American Society of Clinical Oncology/College of American Pathologists proposed several recommendations for human epidermal growth factor receptor 2 (HER2) test standardization. One suggestion was that image analysis (IA) could be useful for scoring of HER2/neu immunohistochemistry. The utilization of IA in a realworld practice in a large cohort of cases has not been previously reported. Objectives.- To compare HER2/neu quantification by IA with gene amplification by fluorescence in situ hybridization (FISH); to determine sensitivity, specificity, and concordance rates with the FISH assay; and to determine association between HER2 status with estrogen receptor (ER), progesterone receptor (PR), and Ki-67 expression. Design.- We evaluated HER2 results performed by immunohistochemistry and FISH in conjunction with ER, PR, and Ki-67 in 3093 invasive breast cancer cases from 2002 to 2011. Results.- The overall concordance between immunohistochemistry and FISH was 87.3% (1768 of 2026). When analyzed by year, there was an improvement in the positive concordance rate from 49.4% (44 of 89) to 95.0% (57 of 60) (P < .001). The negative concordance rate was at least 95% with a median false-negative rate of 1.5%. In the FISH+ group, amplification ratio showed significant correlation with IA scores (P < .001). Positive versus negative HER2 status was associated with lower ER and PR levels (P < .001) and higher Ki-67 expression (P < .001). Conclusion.- Scoring of HER2/neu by IA was associated with high false-positive rates before 2008. Improvement in concordance rate after 2008 may be due to proper tissue handling, improved HER2/neu scoring by IA, and assay standardization.