Problematic aspects of assessing predictive markers for gastric cancer based on endoscopic biopsy samples. Review

An important aspect of the treatment of patients with gastric cancer (GC) is the accurate determination of human epidermal growth factor receptor 2 (HER2) status. HER2-positive cancer of the stomach and gastroesophageal junction is an aggressive molecular subtype of the tumor, detected in 5–20% of cases of adenocarcinoma of this localization. Some problems may arise from incorrect or inaccurate methods of tumor biopsy and formalin fixation, which can be identified as one of the key factors that affect the reliability of HER2 assessment. This article will cover the following aspects: 1) biopsy of histological tissue during endoscopic examination, taking into account localization; 2) the algorithm by which histological tissue is routed in the institution; 3) key points when analyzing the timing of fixation of histological tissue; 4) understanding and assessing the significance of HER2 expression in GC biopsies.