Features of the composite adenoma-microcarcinoid:
(1) The patient has am intestinal adenomatous polyp, typically pedunculated.
(2) There are nests of cells seen within the mucosa and/or submucosa of the polyp, sometimes showing an infiltrative pattern.
(3) The nests are positive for immunoperoxidase stains for neuroendocrine markers (such as synaptophysin).
(4) Some cells may show squamoid features.
Locations where identified:
(1) colon
(2) duodenum
Significance: The nests of cells may be misinterpreted as invasive adenocarcinoma, that could result in additional, unnecessary therapy.
The workup should include grading the carcinoid component based on mitotic activity and Ki-67 index. Very rarely high-grade neuroendocrine carcinomas have been described.
