Is the recent WHO histological classification for gastric cancer helpful for application to endoscopic resection?

Background: Endoscopic resection is performed in undifferentiated-type early gastric cancer (UD-EGC), including poorly differentiated (PD) adenocarcinoma and signet ring cell (SRC) carcinoma. We previously found that different approaches are needed for PD adenocarcinoma and SRC carcinoma for curative resection. However, according to the 2010 WHO classification, diffuse-type PD adenocarcinoma and SRC carcinoma are categorized in the “poorly cohesive carcinomas.” Thus, we assessed whether the WHO classification is helpful when endoscopic resection is performed for treatment of UD-EGC. Methods: We analyzed clinicopathological features of 1295 lesions with SRC carcinoma and PD adenocarcinoma treated by open surgery. We recategorized them into intestinal-type PD adenocarcinomas and poorly cohesive carcinomas (SRC carcinoma, diffuse-type PD adenocarcinoma). We also recategorized 176 lesions treated by endoscopic resection into intestinal-type PD adenocarcinomas and poorly cohesive carcinomas. Results: According to the open surgery data, the rates of lymph node metastasis (LNM) and lymphovascular invasion were significantly lower in SRC carcinoma than in diffuse-type and intestinal-type PD adenocarcinomas. The rates of LNM and lymphovascular invasion were significantly higher in diffuse-type PD adenocarcinoma than in SRC carcinoma. Endoscopic resection data showed no recurrence if the carcinoma was curatively resected. However, the commonest cause of noncurative resection was different in SRC carcinoma and PD adenocarcinoma. A positive lateral margin was the commonest cause in SRC carcinoma versus a positive vertical margin in both intestinal-type and diffuse-type PD adenocarcinoma. Conclusions: The clinical behavior differs in diffuse-type PD adenocarcinoma and SRC carcinoma. On the basis of LNM and outcomes of endoscopic resection, the recent WHO classification may not be helpful when endoscopic resection is performed for treatment of UD-EGC.