Neuroendocrine tumors of the gastro-entero-pancreatic system

Table 1 WHO classification[12]

Site	Well differentiated endocrine tumor		Well-differentiated endocrine carcinoma	Poorly-differentiated endocrine carcinoma
	BB	UB
Pancreas	< 2 cm	≥ 2 cm	Local invasion	Small cells
	< 2 mitoses1	> 2 mitoses	2-10 mitoses	> 10 mitoses
	< 2% Ki-67	> 2% Ki-67	> 5% Ki-67	> 15% Ki-67
	No vascular invasion	Vascular invasion	Vascular invasion ± metastases	Vascular/perineural invasion
Stomach	Mucosa/Submucosa	Mucosa/Submucosa	Invasion of muscularis propria ± metastases	Small cells
	≤ 1 cm	> 1 cm
	No vascular invasion	Vascular invasion
Duodenum/	Mucosa/Submucosa	Mucosa/Submucosa	Invasion of muscularis propria ± metastases	Small cells
Jejunum	≤ 1 cm	> 1 cm
	No vascular invasion	Vascular invasion
Ileum/	Mucosa/Submucosa	Mucosa/Submucosa	Invasion of muscularis propria ± metastases	Small cells
Colon/	≤ 1 cm (ileum)	> 1 cm (ileum)
Rectum	≤ 2 cm (colon)	> 2 cm (colon)
	No vascular invasion	Vascular invasion
Appendix	≤ 2 cm	> 2 cm	Extensive invasion of mesoappendix ± metastases	Small cells
	No vascular invasion	Vascular invasion

¹Mitoses expressed as number/10 high power field. BB: Benign behavior; UB: Uncertain behavior.