Gastric neuroendocrine tumor: A practical literature review

Table 1 Classification of gastroenteropancreatic neuroendocrine tumors according to the World Health Organization 2010

	Grade I	Grade II	Grade III
Tumor size in cm	≤ 2	> 2	Any
Mitoses/10 HPF	< 2	2–20	> 20
Ki 67 index, %	< 3	3–20	> 20
Differentiation	Well differentiated	Well differentiated	Poorly differentiated

Adapted from[18]. HPF: High-power fields.

Table 2 Classification of gastroenteropancreatic neuroendocrine tumors: Neuroendocrine neoplasms according to the World Health Organization 2019

Terminology	Differentiation	Grade	Mitotic rate	Ki 67 index, %
NET, G1	Well differentiated	Low	< 2	< 3
NET, G2	Well differentiated	Intermediate	2-20	3-20
NET, G3	Well differentiated	High	> 20	> 20
NEC, SCNEC	Poorly differentiated	High	> 20	> 20
NEC, LCNEC	Poorly differentiated	High	> 20	> 20
MiNEN	Well or poorly differentiated	Variable	Variable	Variable

Adapted from[17]. NET: Neuroendocrine tumor; NEC: Neuroendocrine carcinoma; SCNEC: Small cell neuroendocrine carcinoma; LCNEC: Large cell neuroendocrine carcinoma; MiNEN: Mixed neuroendocrine non-neuroendocrine neoplasm.

Table 3 Types of gastric neuroendocrine tumors

	Type I	Type II	Type III
Prevalence, %	70-80	5-10	10-20
Background	Chronic atrophic gastritis	Gastrinomas (Zollinger-Ellison syndrome)	Normal mucosa
Other syndromes	Autoimmune polyglandular syndrome	MEN-1 syndrome
Number of lesions	Multiple	Multiple	Single
Site of tumor	Fundus/body	Fundus/body	Fundus/body
Cell of origin	ECL	ECL	ECL, EC or X cell
Serum gastrin levels	Elevated	Elevated	Normal
Gastric PH	High	Low	Normal
Underlying mucosa	Atrophic	Hypertrophic	Normal
Size of tumors, usual	1-2 cm	1 cm	> 2 cm
Invasion	Rare	More common	Common
Metastases
Lymph nodes	5%-10%	10%-20% (duodenal tumors)	50%-100%
Liver	2%-5%	10%	22%-75%
Prognosis	Excellent	Very good	Similar to gastric adenocarcinoma

Adapted from[18]. ECL: Enterochromaffin-like; EC: Endocrine.