Multifocal G1-G2 gastric neuroendocrine tumors: Differentiating between Type I, II and III, a clinicopathologic review

Table 1 Features of Types I, II and III gastric neuroendocrine tumors

	Location	Clinical association	Metastasis	Ki67 proliferation index	Prognosis	Size
Type I	Body	Pernicious anemia; Atrophic Gastritis	Rare	< 3%	Good	Variable < 1-2 cm
Type II	Body	Multiple Endocrine Neoplasia type 1, Zollinger-Ellison syndrome	10%-30% metastasize	< 3%; Rarely 3%-20%	Variable prognosis but overall benign behavior	< 2cm
Type III	Any part of stomach	No clinical association	Very common	3%-20%; Rarely >20%	Aggressive behavior	> 2cm

Table 2 Grading system of well-differentiated neuroendocrine tumors according to the 2017 World Health Organization classification

Neuroendocrine tumor	Mitotic index	Ki67 proliferation index
Neuroendocrine tumor (G1) (well differentiated)	< 2	< 3%
Neuroendocrine tumor (G2) (well differentiated)	2-20	3%-20%
Neuroendocrine tumor (G3) (well	> 20	> 20%