Gastric cancer incidence in Mongolia: A clinical and molecular pathological study.

Abstract

e16101 Background: Gastric cancer (GC) tends to be different in populations and our previous study showed that 66.6% of all early GCs are in cardia, which was totally different from any global data. Japanese data suggested that tendency of GC and its mortality greatly changed within 10 years due to early detection and development of the Endoscopic Submucosal Dissection (ESD). However, GC is still second leading cancer in Mongolia in terms of both mortality and incidence. In this study, we aimed to analyze molecular pathological characterization of advanced GCs in surgical specimens and evaluate result with early GC treatment. Methods: Total of 1435 advanced GC cases of partial and total gastrectomy between 2019-2022, and 198 early GC cases of ESD between 2017-2020 at the National Cancer Center of Mongolia were evaluated in this study. Results: Clinical presentations of advanced GC, age range 18-83 years (average 57), male/female ratio 69.3%/30.7%. Location of the GC in stomach, 46.4% upper (35.3% cardia alone), 33.3% middle, 19% lower and 1.2% was scirrhous. Histology with differentiated or intestinal type 45.6%, poorly differentiated or diffuse 51.1%, mixed 3.3%. Non-epithelial and rare tumors (GIST 20, leiomyoma 5, neuroendocrine 2, squamous 2, schwannoma 1, lymphoma 1), and non-tumor 13 cases were detected which was not included in current study. Total 106 GC cases were evaluated for HER2 by immunohistochemistry (score-0,1+ 86.8%, 2+ 3.8%, 3+ 9.4%). Gene expression was detected in 11% of score-0,1+,2+ cases by in situ hybridization on evaluated cases. 45% of ESD specimens were invasive adenocarcinomas and rest of them were low to high grade dysplasia. Total 4 ESD cases followed by gastrectomy due to recurrence or positive resection margin. Conclusions: In our study, 46.6% of surgical cases of GC were in cardia and upper part of the stomach which was significantly different from similar high incidence countries like Japan and Korea. This may explain we have different etiology and environmental factors for GC in our population. ESD showed high radical resection with low recurrence rate for treatment of early GC in our country. However, number of GC surgical cases are increasing every year and show no tendency of decrease. This may relate to high rate of late-stage diagnosis. In our study, molecular and pathological characterization of GC in Mongolia and its subsite correlation in stomach was similar with other Asian reference data. Gastric Cancer global data comparison by its histology type and location (shown by percentage). Asia Caucasians Africa Latin America United States Mongolia Intestinal type 47.5 53.5 39.6 49.7 55.9 45.6 Diffuse type 46.4 30.8 60.4 36.5 40.5 51.1 mixed type 6.1 15.7 0 13.8 3.7 3.3 Upper part 12.8 15.8 19.1 20.5 10.6 46.4 Middle part 32.8 41.5 30.7 28.2 22.4 33.4 Lower part 54.5 42.7 50.2 51.3 68.2 19 Global data reference: M.J. L ́opez et al. Critical Reviews in Oncology / Hematology 181 (2023) 103841.