nPTD Classification: An Updated Classification of Gastric Cancer Location for Function Preserving Gastrectomy Based on Physiological Lymphatic Flow
Abstract Background: The correlation between tumor location and lymphatic flow distribution in gastric cancer has been previously reported, and PTD (Proximal – Transitional – Distal) classification, proposed. We updated and developed the nPTD classification.Method: We retrospectively studied gastric cancer patients who underwent the dye method sentinel node biopsy from 1993 to 2020. The inclusion criteria were a single lesion type 0 cancer of ≤5 cm in the long axis, clinically node-negative, and invasion within the proper muscle layer pathologically. In this study, the distribution of dyed lymphatic flow was evaluated for each occupied area of the tumor.Results: We selected 416. The tumors located watershed of the right and left gastroepiploic artery near greater curvature had extensive lymphatic flow; therefore, a newly circular region with a diameter of 5 cm is set on the watershed on greater curvature between P and T zone as the ‘n’ zone. In addition, for cancers located in the lesser P curvature, lymphatic flow to the greater curvature was not observed. Therefore, the P zone is divided into two: the lesser curvature side (PL) and the greater curvature side (PG).Conclusions: The advantage of the nPTD classification is that it provides not only proper nodal dissection, but also adequate function-preserving gastrectomy. If the tumor is localized within the PL, the proximal gastrectomy resection area can be further reduced. In contrast, for cancers located in the ‘n’ zone, near-total gastrectomy is required because of the extensive lymphatic flow.