Abstract
Objective: To determine the frequency and expression of HER2/neupositivity by immunohistochemistry in gastric adenocarcinoma.
Methodology: A total of 68 cases of gastric adenocarcinoma were included and Immunohistochemical marker for HER2/neu was applied and evaluated on paraffin sections. HER2/neu overexpression according to age, gender, site and histological type was determined. HER2/neu was assessed on the membrane staining of tumor cells. It was considered positive when more than 10% of the cells stained positively in resection specimens and for biopsy specimens at least 5 cells were positive.
Results:Out of 68 cases, 42 (61.8%) were gastric cardia in origin, 16 (23.5%) of gastoesophageal junction and 10 (14.7%) of gastric fundus. 3+ HER2/neu staining in gastric cardia, gastroesophageal junction and gastric fundus was found to be 6 (14.3%), 6 (37.5%) and 2 (20%), respectively. 36 (52.9%) cases were intestinal type and 32 (47.1%) were signet ring type and 3+ HER2/neu staining was 12 (33.3%), and 2 (6.3%), respectively. There were 3+ positive in 14 (20.6%) cases, 0, 1+ negative in 38 (55.9%) cases and 2+ equivocal in 16 (23.5%).
Conclusion: HER2/neuoverexpression can be determined in gastric adenocarcinoma by using immunohistochemistry. Approximately 21% cases showed overexpression in our study. Larger studies are required for more definitive results to accurately determine proportion of patients who may benefit from trastuzumab therapy.

Key words: Gastric adenocarcinoma, HER2 /neu, Immunohistochemistry.