HER2 status assessment in carcinomas of various localizations. A multicenter morphological study in the Russian Federation

HER2 is a clinically significant predictive and prognostic marker in a number of epithelial malignant neoplasms. With the introduction of HER2-targeted therapeutic approaches, including antibody-drug conjugates, the need for standardized assessment of HER2 status in tumors of various localizations has become increasingly important. Objective. To assess the prevalence of HER2-positive tumors (IHC 3+) in epithelial malignant neoplasms of various localizations in the Russian population using a unified diagnostic approach. Material and methods. This multicenter study included 1.511 tumor tissue samples from patients with epithelial malignant neoplasms of various localizations, obtained from reference pathology centers of the Russian Federation. HER2 status was determined by immunohistochemistry using anti-HER2 antibody (clone 4B5, Ventana) and standardized interpretation criteria developed for gastric cancer and gastroesophageal junction cancer. In cases of equivocal HER2 status (IHC 2+), in situ hybridization was recommended. Results. HER2-positive tumors (IHC 3+) were identified in the majority of the analyzed localizations, with prevalence varying widely depending on tumor type. The highest frequency of HER2 positivity was observed in urothelial carcinoma of the urinary bladder, as well as in gastric and gastroesophageal junction cancers. No HER2-positive cases were detected in lung adenocarcinoma or pancreatic cancer. Conclusion. The study results confirm the reproducibility of HER2 status assessment using a unified diagnostic approach in a multicenter setting. The application of standardized HER2 interpretation criteria ensures data comparability and provides a methodological basis for further clinicopathological studies and for the implementation of HER2-targeted therapeutic strategies in clinical practice.