Background: Endoscopic resection (endoscopic mucosal resection, EMR, and endoscopic submucosal dissection, ESD) has been accepted worldwide as a less invasive standard treatment for early gastric cancer (EGC). However, the risk of synchronous and metachronous gastric cancer developing in the post-endoscopic resection patient has become a major problem. We investigated the incidence and characteristics of synchronous and metachronous multiple gastric cancers in a retrospective study of patients with EGC after endoscopic resection. Patients and Methods: We studied the clinicopathological features of 235 patients with EGC who had undergone endoscopic resection and were periodically followed up using endoscopic examinations (181 with a single lesion, 34 synchronous multiple lesions, and 20 metachronous multiple lesions). Results: The overall incidence of synchronous and metachronous multiple gastric cancer was 14.5 and 8.5%, respectively, during a follow-up of 12-77 (median 26.5) months. Undifferentiated histology of the primary lesion was related to the occurrence of synchronous gastric cancer (p < 0.001). Undifferentiated histology and upper location of the primary lesion were correlated with the occurrence of metachronous gastric cancer (p = 0.002, 0.001). Most synchronous and metachronous lesions were well to moderately differentiated (82.4 and 80.0%); however, the proportion with undifferentiated histology (including poorly differentiated carcinoma and signet ring cell carcinoma) in synchronous and metachronous gastric cancer was significantly higher than in single gastric cancer (p = 0.008). Conclusions: Undifferentiated histology of EGC may predict the occurrence of synchronous and metachronous lesions after endoscopic resection.
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