-Case Reports-

Adenocarcinoma and Neuroendocrine Collision Tumor in a Giant Gastric Hyperplastic Polyp

Yoo Min Park¹, Kiyong Na², Ji-Youn Sung², Jae-Young Jang¹ and Youn Wha Kim²

¹Division of Gastroenterology and Hepatology, Department of Internal Medicine, Kyung Hee University College of Medicine, Seoul, Republic of Korea
²Department of Pathology, Kyung Hee University Hospital, Kyung Hee University College of Medicine, Seoul, Republic of Korea

Screening esophagogastroduodenoscopy of a 65-year-old man revealed a 4.7-cm polypoid in the gastric high body. Clinical and laboratory findings, including serum gastrin level (460 pg/mL) and biopsy findings, were consistent with a diagnosis of type I neuroendocrine tumor (NET). Histologically, the mass consisted of dilated tortuous glands at the surface and grade 1 NET in deeper tissue. Some hyperplastic glands exhibited a transition to adenocarcinoma, which invaded the NET, simulating a "tumor in tumor" appearance. Next-generation sequencing revealed that the adenocarcinoma component harbored a TP53 mutation, whereas the NET component showed no pathogenic mutation. To our knowledge, this unusual collision of adenocarcinoma and NET within a single gastric hyperplastic polyp has not been previously described. This case suggests that large gastric hyperplastic polyps should be carefully examined because of the possibility of underlying NET and malignant transformation of surface epithelium.

J Nippon Med Sch 2020; 87: 157-161

Keywords
hyperplastic polyp, neuroendocrine tumor, adenocarcinoma, stomach

Correspondence to
Kiyong Na, Department of Pathology, Kyung Hee University Hospital, Kyung Hee University College of Medicine, 26 Kyungheedae-ro Dongdaemun-gu, Seoul, 02447, Republic of Korea
raripapa@gmail.com

Received, December 6, 2019
Accepted, January 21, 2020