Stomach - NET G1 (Carcinoid tumor)

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Stomach

Carcinoma

NET G1 (Carcinoid tumor)

Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 31 August 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

Clear cell variant, ECL cell, gastrin producing

General
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● WHO defines as well-differentiated neuroendocrine tumor (NET) composed of cells with features similar to those of normal gut endocrine cell, expressing general markers of neuroendocrine differentiation (usually diffuse and intense chromogranin A and synaptophysin) and hormones (usually intense but not necessarily diffuse) according to site, with mild- to-moderate nuclear atypia and a low number of mitoses (PubCan)
● Proposed grading:
– G1 (NET G1): mitotic count <2 per 10 high power fields (HPF) or Ki67 index <=2%
– G2 (NET G2): mitotic count 2–20 per 10 HPF or Ki67 index 3–20%

Clinical features
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● Slow growing
● Associated with achlorhydria, antral G cell hyperplasia, hypergastrinemia, diffuse enterochromaffin-like cell hyperplasia (Am J Surg Pathol 1987;11:909, Am J Surg Pathol 1987;11:435)

Subclassification
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Enterochromaffin-like (ECL) cells:
● Non-peptide secreting endocrine cell of gastric fundus/body mucosa
● Comprises 30% of endocrine cells
● Releases histamine in response to gastrin production by G cells
● Long term gastrin stimulation causes ECL hyperplasia

Type 1 gastric endocrine tumor:
● In patients with autoimmune chronic atrophic gastritis (Am J Surg Pathol 1995;19(S1):S20)
● Occur in 5-10%, usually women, mean age 63 years
● Arise due to enterochromaffin-like cell hyperplasia and hypergastrinemia secondary to parietal cell loss, in fundus/body
● 57% multifocal
● 97% < 1.5 cm
● 91% limited to mucosa or submucosa
● Only 2-5% associated with liver metastases
● Nearly always grade 1, indolent course, almost never causes death

Type 2 gastric endocrine tumor:
● In patients with Zollinger-Ellison syndrome, usually also MEN1 (abnormality of menin gene on 11q13)
● No gender predilection, mean age 50 years
● Associated with ECL cell hyperplasia and hypergastrinemia
● Usually multicentric in body/fundus
● 23% > 1.5 cm, 30% with local nodal metastases, 10% with liver metastases
● Death more likely from gastrinomas of Zollinger-Ellison syndrome than from the carcinoid tumors

Type 3 gastric endocrine tumor:
● Sporatic, not related to hypergastrinemia or ECL cell hyperplasia
● Usually solitary, may not be in body/fundus
● 74% in men, mean age 55 years
● 76% deeply invasive, 71% have nodal metastases, distant metastases common

Type 4 gastric endocrine tumor:
● Very rare, due to defective gastric acid secretion
● Metastases only to regional lymph nodes and liver, but patients may still have long term survival

Case reports
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● Carcinoid tumors with adenocarcinoma (Arch Pathol Lab Med 1991;115:1006, Arch Pathol Lab Med 1988;112:91

Treatment
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● Antrectomy (removes gastrin stimulation, Arch Pathol Lab Med 1994;118:658)
● Excision of tumors

Gross description
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● Small, sharply outlined, covered by flattened mucosa
● Resemble polyps

Micro description
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● Glandular, trabecular or rarely insular patterns
● Bland nuclei with salt and pepper chromatin, rare mitotic figures, prominent vessels, no necrosis

Positive stains
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● Chromogranin, keratin, neuron-specific enolase

Negative stains
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● CK7, CK20 (Hum Pathol 2001;32:1087)

Electron microscopy description
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● Dense core secretory granules

Clear cell variant

Case reports
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● 75 year old woman with tumor composed entirely of clear cells with foamy cytoplasm (Arch Pathol Lab Med 1997;121:1100)

Gross description
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● Yellow, resembles gastric xanthoma

Micro description
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● Uniform clusters of polygonal cells with foamy cytoplasm
● Abundant vascular stroma

Positive stains
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● Chromogranin A

Electron microscopy description
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● Dense core neurosecretory granules

ECL cell NETs (Enterochromaffin-like cell neuroendocrine tumors)

General
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● Tropic effect from gastrin, related to long-standing elevated gastrin levels from gastrinoma or gastric gastrin cells responding to achlorhydria
● Multiple, polypoid, throughout fundus
● Usually associated with ECL-cell hyperplasia and may be difficult to distinguish from hyperplasia

Micro description
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● Smooth muscle proliferation, associated with atrophic gastritis with intestinal metaplasia

Gastrin producing NET (Gastrinoma)

General
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● Solitary, usually in antrum, more common in duodenum

Positive stains
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● Gastrin, however, gastrin staining in the absence of sequelae of Zollinger Ellison syndrome is insufficient to diagnose Gastrin producing NET
● ACTH-producing NET is very rare

End of Stomach > Carcinoma > NET G1 (Carcinoid tumor)

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