Clinico-pathologic characteristics of sub-epithelial tumor (SET) like gastric cancers.

It has been known that sub-epithelial tumor (SET)-like gastric cancer (GC) is a special type of gastric cancer with a relatively low prevalence of approximately 1%. Most of the studies are old and would be underestimated. Recently, the application of endoscopic ultrasound has increased, so its frequency is expected to increase. A consecutive study was undertaken from March 2020 to March 2024, and we analyzed 380 GC tissues (194 early GCs; 186 advanced GCs) from the patients who had received gastrectomy or endoscopic submucosal dissection. Through picture archiving and communication system, the endoscopic findings at the time of diagnosis were analyzed. After removal, molecular biological characteristics were examined. The prevalence of SET like GC was 5.8% (22/ 380) endoscopically. There were no differences between the SET like GC and the other group with respect to gender, smoking, drinking history, and Helicobacter pylori infection. SET like GC patients were statistically older (P = 0.04). The frequency of advanced GC (P = 0.03) and the frequency of microsatellite instability (MSI) (P < 0.01) were statistically higher in SET like GC. Exceptional cases included Epstein-Barr virus-associated lymphoepithelioma-like carcinoma, undifferentiated carcinoma with rhabdoid features, mixed neuroendocrine tumor, case with gastritis cystica profunda, and cases that used anti-ulcer drugs or responded to chemotherapy. It also appeared in gastric cancer with confirmed genetic predisposition. SET like GC had many advanced cases and MSI-positive GCs. If we investigate various exceptional cases, it is likely that their frequency will continue to increase. We urgently need measures to address this.