Undifferentiated early gastric cancer diagnosed as differentiated histology based on forceps biopsy

Histological diagnosis before endoscopic resection (ER) is important to determine whether ER should be performed; indeed, the use of ER for undifferentiated early gastric cancer (UD-EGC) remains controversial. The aim was to investigate the clinicopathological features of UD-EGC in ER specimens, diagnosed as differentiated histology based on biopsy. 289 patients with EGC were treated by ER. Among them, 13.1% were diagnosed as UD-EGC after ER, and 18.4% of them showed differentiated histology based on biopsy before ER. We analyzed UD-EGC with differentiated histology (D-group) compared to undifferentiated histology (UD-group) on biopsy. The D-group showed moderately differentiated adenocarcinoma on biopsy and poorly differentiated adenocarcinoma in ER specimens. The D-group was significantly associated with older age, intestinal metaplasia in the surrounding mucosa, and larger size than the UD-group. Gland portion of tumor, mixed-type Lauren classification, submucosal invasion, lymphovascular invasion, and perineural invasion were more common in the D-group than in the UD-group. The number of biopsies was not different between the groups. When comparing the histopathological mapping findings and endoscopic appearances of the D-group, the zone of transition from differentiated to undifferentiated histology was frequently found on one or two peripheral sides of the lesion. In conclusion, areas of EGC greater than 20mm with moderately differentiated histology on biopsy may contain an undifferentiated component. UD-EGC with differentiated histology on biopsy may show more aggressive behavior than UD-EGC, consistent with the biopsy pathology. Biopsy at several peripheral sides of the lesion may be helpful for diagnosis of UD histology before treatment.