Wong RWC, et al. - Researchers sought to report 9 cases (aged 32 to 85) of endometrial mucinous lesions showing gastric (gastrointestinal)-type features by morphology and immunohistochemistry. These cases comprised 4 adenocarcinomas and 5 benign mucinous lesions. Gastric-type morphology was noted in all 4 cases of adenocarcinomas and goblet cells were observed in 1 adenocarcinoma case, with a component of benign gastric-type mucinous glands in 1 adenocarcinoma case. The adenocarcinomas were immunohistochemically positive for CK7 (4/4), CEA (4/4), MUC6 (3/3), PAX8 (3/4), CK20 (2/4), CDX2 (2/4), and estrogen receptor (1/4) and negative for Napsin A (0/3), with mutation-type p53 staining in 2/4 cases, block-type p16 positivity in 1/4, and scattered chromogranin-positive cells in 1/2. Follow-up revealed aggressive behavior. Among cases with benign mucinous lesions (including the benign component in 1 adenocarcinoma), they identified gastric-type morphologic features in 5/6 cases, goblet cells in 5/6, and Paneth-like neuroendocrine cells in 1/6. An endometrial polyp was observed in 5/6 cases with benign mucinous lesions. The benign mucinous lesions were immunohistochemically positive for CK7 (5/5), CDX2 (5/6), estrogen receptor (4/5), MUC6 (4/5), CK20 (3/5), PAX8 (3/5), and CEA (2/4), with scattered chromogranin-positive cells in 4/4 cases. In all cases, Napsin A was tested negative, p53 was wild-type and p16 was negative. For this distinctive group of rare aggressive endometrial carcinomas, the term “endometrial gastric (gastrointestinal)-type adenocarcinoma” is proposed by researchers. Benign or atypical gastric (gastrointestinal)-type mucinous lesions are identified to be putative precursors for these adenocarcinomas, comparable to recognized premalignant gastric-type lesions in the cervix and the vagina. For understanding their pathogenesis and clinical significance, future recognition and reporting of these gastric-type endometrial mucinous lesions will be help helpful.