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World J Gastrointest Endosc. Dec 16, 2021; 13(12): 593-606
Published online Dec 16, 2021. doi: 10.4253/wjge.v13.i12.593
Composite intestinal adenoma-microcarcinoid: An update and literature review
Zhi-Yan Fu, Michel Kmeid, Mahmoud Aldyab, Stephen M Lagana, Hwajeong Lee
Zhi-Yan Fu, Michel Kmeid, Mahmoud Aldyab, Hwajeong Lee, Pathology and Laboratory Medicine, Albany Medical Center, Albany, NY 12208, United States
Stephen M Lagana, Department of Pathology and Cell Biology, Columbia University Irving Medical Center, New York, NY 10032, United States
Author contributions: Fu ZY carried out the study including review of the literature, and drafted the manuscript, gave final approval of the version to be published; Kmeid M, Aldyab M and Lagana SM contributed to the editing and critical review of the manuscript, as well as final approval of the version to be published; Lee H provided cases for microscopic images, edited and critically reviewed the manuscript, and approved the final version to be published; all authors are agreeable to be accountable for all aspects of the work.
Conflict-of-interest statement: The authors declare no conflict of interest.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Hwajeong Lee, MD, Associate Professor, Pathology and Laboratory Medicine, Albany Medical Center, 43 New Scotland Ave, Albany, NY 12208, United States.leeh5@amc.edu
Received: March 12, 2021
Peer-review started: March 12, 2021
First decision: October 17, 2021
Revised: October 19, 2021
Accepted: November 26, 2021
Article in press: November 26, 2021
Published online: December 16, 2021
Processing time: 276 Days and 8.4 Hours
Abstract

Composite intestinal adenoma-microcarcinoid (CIAM) is a rare intestinal lesion consisting of conventional adenoma and small, well differentiated carcinoid [microcarcinoid (MC)] at its base. The incidence of CIAM is 3.8% in surgically resected colorectal polyps. While its pathogenesis is unknown, studies support the role of Wnt/β-catenin pathway in the tumorigenesis of CIAM. CIAMs have been primarily reported in the colon wherein they present as polyps with well-defined margins, similar to conventional adenomatous polyps. MC is usually found in adenomatous polyps with high-risk features such as large size, villous architecture, or high grade dysplasia. Histologically, the MC component is often multifocal and spans 3.9 to 5.8 millimeters in size. MC is usually confined within the mucosa but occasional CIAM cases with MC extending to the submucosa have been reported. MC of CIAM demonstrates bland cytology and inconspicuous proliferative activity. The lesional cells are positive for synaptophysin and 60% to 100% of cases show nuclear β-catenin positivity. MC poses a diagnostic challenge with its morphologic and immunohistochemical resemblance to both benign and malignant lesions, including squamous morules/metaplasia, adenocarcinoma, squamous cell carcinoma, sporadic neuroendocrine tumor and goblet cell adenocarcinoma. CIAM is an indolent lesion with a favorable outcome. Complete removal by polypectomy is considered curative. Awareness and recognition of this rare entity will help arrive at correct diagnosis and improve patient care. Currently, CIAM is not recognized as a subtype of mixed neuroendocrine-non-neuroendocrine neoplasm by WHO.

Keywords: Composite; Adenoma; Microcarcinoid; Composite intestinal adenoma-microcarcinoid; Wnt/β-catenin; Mixed neuroendocrine-non-neuroendocrine neoplasm

Core Tip: Composite intestinal adenoma-microcarcinoid (CIAM) is a rare intestinal lesion consisting of adenoma and well differentiated microcarcinoid components. While it is a form of mixed neoplasm with both neuroendocrine and non-neuroendocrine elements, CIAM is currently not recognized as a distinct subtype of mixed neoplasm by WHO. It is found incidentally during the pathologic examination of adenomatous polyps. Altered Wnt/β-catenin pathway appears to play a role in its pathogenesis. Other benign and malignant lesions need to be distinguished from CIAM given differing therapeutic implications. CIAM is an indolent disease with a favorable outcome.