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Small bowel (small intestine)

Other malignancies

Carcinoid tumor

Reviewer: Hanni Gulwani, M.D. (see Reviewers page)
Revised: 22 December 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Low grade malignancy arising from epithelial stem cells in crypts
● Also called Neuroendocrine G1 (NET G1) tumor (WHO)

Clinical features

● 50% of small bowel tumors
● Usually adults in 50ís, also children
● Most common in ileum (including Meckelís diverticulum); also jejunum and distal duodenum
● Associated with celiac disease, bowel duplication, von Recklinghausenís disease, inflammatory polyps
● 15-35% are multiple
● Slow growing, but can metastasize to regional lymph nodes, liver, bone, skin, thyroid
● Usually occur as small, dispersed nodules
Carcinoid syndrome in 1% (20% with widespread metastases)
● 5 year survival: 50-65% (85% if confined to bowel wall vs. 5% if serosal invasion)

Clinical features by Site

● Patients with multiple tumors have higher incidence of carcinoid syndrome (22% vs. 2%) and poorer prognosis (Am J Surg Pathol 2003;27:811)

● 2/3 express gastrin, 1/3 of these are associated with Zollinger-Ellison syndrome and are almost always metastatic
● May be associated with MEN1
● Duodenal carcinoids are less aggressive, usually donít cause death vs. ampullary carcinoids (Hum Pathol 2001;32:1252)

Case reports

● 55 year old man with angiomatous polyps simulating Crohnís disease (Arch Pathol Lab Med 2000;124:450)
● 59 year old woman with metastases to cardiac conducting system (Arch Pathol Lab Med 2002;126:1538)


● Surgical excision of tumor and regional lymph nodes, excise solitary liver metastases

Gross description

● Tumor protrudes through mucosa as small, polypoid lesion, intact or ulcerated overlying mucosa, buckling of bowel wall
● Bright yellow after formalin fixation, mean 2 cm

Gross images

Carcinoid tumors

Micro description

● Submucosal tumor that infiltrates muscularis propria
● Solid, insular (nesting), trabecular or glandular masses of monotonous small round cells with peripheral pallisading
● Moderate finely granular cytoplasm, small nucleoli, salt and pepper chromatin
● Angiolymphatic invasion common, mitotic figures rare
● Mucin present if glandular pattern
● Amphicrine cell pattern rare (endocrine and exocrine cells)
● Adjacent mucosa in ileal tumors shows angiomatous polyposis (mucosal edema, capillary ectasia, muscularis mucosa hypertrophy, fibrosis / smooth muscle proliferation in lamina propria, club-shaped villi, intramucosal capillary proliferation, although this is not specific for carcinoid tumors, Mod Pathol 2001;14:821)

Micro images

Carcinoid tumors

With adjacent angiomatous polyposis

Ileal biopsy (courtesy of Dr. Hanni Gulwani)

Ileal biopsy (courtesy of Dr. Hanni Gulwani) - synaptophysin

Positive stains

● Keratin, CEA, chromogranin, synaptophysin, Leu7, Fontana-Masson (argentaffin reaction)
● Also neuroendocrine secretory protein 55, Ghrelin, somatostatin receptor, CDX2, xenin, CK19 (Arch Pathol Lab Med 2008;132:1285)
● PAX8 (paired box) is expressed in duodenal carcinoids and negative in ileal carcinoids (Am J Surg Pathol 2010;34:723)
● Ileal carcinoid are positive for CDX2 and duodenal carcinoid are positive for PDX-1 (duodenal homeobox factor-1, Am J Surg Pathol 2009;33:626)
● Rarely PAP

Negative stains

● Mucin, S100, CK7, CK20, TTF1

Electron microscopy description

● Well formed, membrane bound, dense core secretory granules with dense (osmophilic) cores

End of Small bowel (small intestine) > Other malignancies > Carcinoid tumor

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