The role of determining HER2neu status in patients with gastric cancer.

e16067 Background: Over the past two decades, gastric cancer has continued to maintain a leading position in both incidence and mortality rates among all malignant neoplasms in the Republic of Kazakhstan. Recent data indicate that amplification or overexpression of the HER2 gene is detected in 7-34% of gastric cancer cases, significantly impacting treatment outcomes. Studying a specific group of patients with HER2 overexpression in gastric cancer is of great interest in clinical oncology. Research aim: To examine the long-term treatment outcomes in patients with gastric cancer depending on the status and level of HER-2 expression in real clinical practice. Methods: Analysis was conducted on 172 formalin-fixed paraffin-embedded samples of gastric adenocarcinoma and gastroesophageal junction carcinoma, subjected to immunohistochemical examination to determine HER2 protein expression. Patients' ages ranged from 18 to 85 years, with a mean age of 61.7 years; among them, 106 (61.6%) were male and 66 (38.4%) were female. Of the 172 patients, 64 (37.2%) had primary tumors located at the gastroesophageal junction, while 108 (62.8%) had tumors located in the body of the stomach. Based on differentiation grade, the majority were G3-100 (50%), G2-91 (45%), G1-9 (5%). HER2 testing was performed on the Ventana BenchMark Ultra platform using the HER2 (4B5) antibody. Results: HER2 overexpression was detected in 26 (15.1%) of the 172 patients. Patients with HER2 2+ non-amplified were 6 (3.5%), HER2 2+ amplified were 8 (4.6%), HER2 1+ was detected in 19 (11%) cases, and HER2 0 was found in 121 (80.9%) cases. Long-term results revealed statistically significant differences, notably the highest overall survival rate in patients with HER-2 overexpression compared to HER-2 low and absence of HER-2. The HER2 3 (+FISH/SISH) variant was significantly more prevalent in 84.6% compared to HER2 0 in 52%, and HER2 1 in 48%, p < 0.05. Comparison of Her2 status using the chi-square method in groups revealed probable differences concerning tumor localization, with a criterion value of 0.034; morphological form (criterion value = 5.83); and differentiation grade (criterion value = 10.05). Conclusions: These results underscore the importance of further HER2 research in gastric cancer and gastroesophageal junction carcinoma for the development of personalized therapeutic strategies.