Yasemin AKCA
The European Research Journal - 2026;12(9):944-950
Objective: Human epidermal growth factor receptor 2 (HER2) is a key molecular driver involved in tumor proliferation and survival and a well-established therapeutic target in breast cancer, while its role in gastrointestinal adenocarcinomas remains heterogeneous and continues to evolve. This study aimed to evaluate HER2 expression patterns and positivity rates in gastric and colorectal adenocarcinomas encountered in routine pathology practice. Methods: Pathology records of gastric and colorectal adenocarcinomas diagnosed between January 2015 and January 2025 were reviewed retrospectively. A total of 124 gastric and 122 colorectal adenocarcinoma cases were included. HER2 immunohistochemical staining results were reassessed and categorized as 0, 1+, 2+, or 3+. Equivocal (2+) cases were further evaluated using available in situ hybridization (ISH) data. Results: HER2 positivity was identified in 4.8% of gastric adenocarcinomas and 3.3% of colorectal adenocarcinomas. This difference was not statistically significant ( P = .75). In gastric cancers, HER2 positivity was more frequently observed in intestinal-type tumors (7.1%) compared with diffuse-type tumors (1.9%), although this difference did not reach statistical significance ( P = .22). No HER2 amplification was identified in equivocal gastric cases. In colorectal carcinomas, HER2 positivity was limited to the conventional adenocarcinoma subtype. Conclusions: HER2 expression is present in a small subset of gastric and colorectal adenocarcinomas and was more frequently observed in intestinal-type gastric adenocarcinomas than in diffuse-type tumors. These findings provide descriptive data regarding HER2 expression patterns in gastrointestinal adenocarcinomas encountered in routine pathology practice and contribute to the existing literature on HER2 expression in these malignancies.
