Poorly differentiated is more significant than signet ring cell component for lymph node metastasis in mixed-type early gastric cancer: a retrospective study from a large-volume hospital

OBJECTIVE: The purpose of this study was to explore the role of different undifferentiated components in the lymph node metastasis (LNM) of early mixed gastric cancer. METHODS: A total of 1596 patients with EGC who underwent gastrectomy were divided into four types: pure differentiated (PD), pure poorly differentiated (Poorly D), pure signet ring cell carcinoma (SRC), and mixed. Mixed type was classified into four subtypes: differentiated-predominant type mixed with poorly differentiated component (MD-P), poorly differentiated-predominant type mixed with differentiated component (MP-D), differentiated-predominant type mixed with SRC component (MD-S), and poorly differentiated-predominant type mixed with SRC component (MP-S). We analyzed the clinicopathological differences between all types and the rates of LNM of patients fulfilling endoscopic submucosal dissection (ESD) criteria. RESULTS: LNM was more common in mixed (21.9%) than in PD (7.5%, P < 0.001) or SRC (11.3%, P < 0.001). When analyzed the subgroups of mixed type, LNM was more frequent in MD-P (15.4%) than in PD (7.5%, P = 0.003). LNM in MD-S (7.4%, P = 1.000) was not higher than in PD. MP-S (24.5%) showed a higher rate of LNM than SRC (11.3%, P < 0.001) rather than Poorly-D (22.7%, P = 0.681). For lesions satisfying ESD criteria, MD-S (0%, P = 1.000), and MD-P (5.9%, P = 0.12) did not have higher rates of LNM than PD (1.4%). CONCLUSION: The presence of poorly differentiated component but not SRC increases the LNM rate of mixed type. ESD is recommended for the treatment of MD-S and MD-P consistent with ESD criteria.