Analysis of Human Epidermal Growth Factor Receptor 2 (HER2) Heterogeneity at the Protein and Gene Levels in Endometrial Cancer: Refining HER2 Reporting and HER2-Directed Therapies
Targeted therapy directed against human epidermal growth factor receptor 2 (HER2) has shown promising results in HER2-positive endometrial cancer. Recent limited data suggest significant intratumoral heterogeneity in HER2 expression in serous carcinomas. We aimed to evaluate HER2 heterogeneity at the protein and gene levels and the impact of variable definitions in endometrial carcinomas including nonserous subtypes. We retrospectively identified biopsies and surgical specimens with available HER2 immunohistochemical (IHC) stains and fluorescence in situ hybridization (FISH) results. IHC stains and FISH data were reevaluated to assess variability in the HER2 protein expression and gene amplification. The overall HER2-positivity rate was 31% using the endometrial criteria, and 42.6% by the gastric criteria. Heterogeneous IHC staining was observed in 45.7% of tumors, predominating in 2+/3+ scores (P < .001). Re-evaluation of FISH revealed a 31% rate of heterogeneous gene amplification. Our study demonstrates a high frequency of HER2 heterogeneity at both the protein and the gene levels. Further studies on HER2 heterogeneity and treatment response are warranted for refining standardized testing and reporting algorithms.