Abstract 134: Lymph node metastases are seeded via two distinct ways in phylogenetic study of gastric cancer

Abstract

Abstract Backgrounds: Gastric cancer (GC) ranked 5th and 8th on the list of cancer related deaths worldwide and in Taiwan, respectively. Due to its high frequency of lymph node spread, lymph node dissection has become a standard procedure in surgical treatment. A randomized trial showed that patients who underwent D2 lymphadenectomy had a better 5-year survival outcome than ones who had D1 dissection in advanced gastric cancer, implying the D2 lymph node might serve as an outpost before tumor cells spread to distant organs. This clinical observation raises a possibility that the regional lymphatic spread could be under strict selection but not a passive process. Materials and Methods: To understand the evolutionary relationship between primary tumors, perigastric lymph nodes, and second tier of lymph nodes in the extra-perigastric area, we reconstruct their phylogeny using genetic variants in hypermutable DNA regions where the mutation rate is 102~104-fold than unique sequence. We have assembled a cohort of 10 gastric cancer patients, including intestinal-, diffuse- and mixed type GC. For each case, we collected all workable lymph node metastases and intensely sampled primary tumors. On average, we have over fifteen samples per case on the phylogenetic tree. Results: Preliminary data of the first two patients show high heterogeneity within primary tumors as well as between different lesions of lymph nodes or peritoneal metastases in gastric cancer. Interestingly, in stark contrast to all other lymph node metastases which intermingle with primary tumors, a clade consisting of one proximal and one distal lymph node with a bootstrap value above 90% is observed in each phylogeny, and it is worth noting that samples on these clades are from intestinal type tumor. Conclusion: Our results indicate that most tumor cells arrive both regional and distal lymph nodes passively via lymphatic drainage in GC while a selective process also exists which coincides with clinical observation. Whether the existence of tumor cells under a relatively stricter selection process would lead to different clinical outcomes is under investigation. Citation Format: Pei-Chi Cheng, Wei-Ting Hung, Yung-Ming Jeng, I-Rue Lai. Lymph node metastases are seeded via two distinct ways in phylogenetic study of gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 134.