Small-Cell Type, Poorly Differentiated Neuroendocrine Carcinoma of the Gallbladder: A Case Report and Review of the Literature

Table 1

WHO classification for neuroendocrine tumors arising in the GI tract.

Differentiation	Grade	Mitotic count	Ki-67 index	Traditional	ENETS, WHO
Well differentiated	Low grade (G1)	<2 per 10 HPF	<3%	Carcinoid, islet cell, pancreatic (neuro)endocrine tumor	Neuroendocrine tumor, G1
	Intermediate grade (G2)	2 to 20 per 10 HPF	3 to 20%	Carcinoid, atypical carcinoid, islet cell, pancreatic (neuro)endocrine tumor	Neuroendocrine tumor, G2
Poorly differentiated	High grade (G3)	>20 per 10 HPF	>20%	Small-cell carcinoma	Neuroendocrine carcinoma, G3, small cell
				Large-cell neuroendocrine carcinoma	Neuroendocrine carcinoma, G3, large cell

ENETS: European Neuroendocrine Tumor Society; WHO: World Health Organization; HPF: high-power fields.