Two Updates on Oesophagogastric Junction Adenocarcinoma from the Fifth WHO Classification of Tumors of the Digestive System: Alteration of Definition and Emphasis on HER2 Test.

Abstract Background: The incidence of oesophagogastric junction adenocarcinoma has increased rapidly but remains controversial over the last decades. There are two crucial updates of the fifth World Health Organization(WHO) classification, including the alteration of its definition and the emphasize on human epidermal growth factor receptor 2 (HER2) test.Methods: A total of 566 clinicopathological samples from patients who were diagnosed with gastric adenocarcinoma were retrospectively analyzed. We comprehensively compared the clinicopathological features of oesophagogastric junction adenocarcinoma between fourth (V4.0) and fifth (V5.0) WHO version. The clinicalpathological features among oesophagogastric junction, proximal and distal gastric tumors with fourth and fifth edition were also compared, respectively. Besides, we discussed the correlation of the HER2-expression with clinicopathological features according to the V5.0. Results: The results showed that the difference was mainly between oesophagogastric junction and distal adenocarcinoma in V4.0, while some were found between proximal and distal adenocarcinoma in V5.0. Tumors invading oesophagus more than 3cm were still mainly oesophagogastric junction tumors. The expression of HER2 in oesophagogastric junction and proximal gastric adenocarcinoma was still higher than that in gastric body and distal site.Conclusions: The clinicopathological parameters of the oesophagogastric junction tumors changed to some extent in the updated WHO version. The proximal gastric tumors tended to be more invasive, rather than that located in oesophagogastric junction. But the latter with oesophageal invasion required additional management. The HER2-expression of oesophagogastric junction adenocarcinoma is the highest. The classification of the V5.0 is reasonable and worth a recommendation.