Optimal Cutoff Size of Large Borrmann Type III Gastric Cancer: Is 8 cm Accurate in Predicting Survival and Incidence of Peritoneal Metastasis?

Background: Large type III gastric cancer (GC) ≥ 8 cm has conventionally been categorized with type IV GC in Japan, leading to alternative treatment strategies such as neoadjuvant chemotherapy and staging laparoscopy (SL). However, whether 8 cm is the correct cutoff remains unclear. Methods: We retrospectively analyzed patients clinically diagnosed with advanced GC who underwent surgery at our department. Patients were classified by Borrmann type, and clinicopathological characteristics including survival outcomes and peritoneal metastasis incidence were analyzed based on tumor size to determine the optimal cutoff for large type III GC. Results: Tumor size correlated with overall survival in type III GC. Although hazard ratios (HRs) for "large" and "small" type III vs. type IV remained comparable up to the 8 cm cutoff (0.60 and 0.41, respectively), HR for "large" type III GC increases sharply to 0.74 with a 10 cm cutoff. Subgroup analysis based on histological subtype revealed similar results in the undifferentiated type. Conversely, a larger cutoff value appeared more appropriate for the differentiated type. The largest difference in the incidence of peritoneal metastasis was observed with a 6 cm cutoff (36.1% in "large" type III and 10.2% in "small" type III), and similar results were observed in the undifferentiated type at the same cutoff. Conclusions: In terms of survival, a 10 cm cutoff may more accurately define large type III GC than the conventional 8 cm. However, if surgeons intend to identify peritoneal metastasis by SL, type III GC ≥ 6 cm could be a possible candidate.