Table 1 NEN 2018 WHO proposed classification of selected NEN by site, category, family, and tumor type

Site	Category	Family	Type	Grade	Current terminology
Lung	Neuroendocrine neoplasm (NEN)	Neuroendocrine tumor (NET)	Pulmonary neuroendocrine tumor (NET)^a	G1 G2	Carcinoid Atypical carcinoid^a
		Neuroendocrine carcinoma (NEC)	Small cell lung carcinoma (Pulmonary NEC, small cell-type)^b		Small cell lung carcinoma
		Neuroendocrine carcinoma (NEC)	Pulmonary NEC, large cell-type		Large cell NE carcinoma
Uterus (corpus and cervix)	Neuroendocrine neoplasm (NEN)	Neuroendocrine tumor (NET)	Uterine neuroendocrine tumor (NET)	G1 G2 G3	Carcinoid Atypical carcinoid Atypical carcinoid
		Neuroendocrine carcinoma (NEC)	Uterine NEC, small cell-type		Small cell carcinoma
		Neuroendocrine carcinoma (NEC)	Uterine NEC, large cell-type		Large cell NE carcinoma
Pancreas	Neuroendocrine neoplasm (NEN)	Neuroendocrine tumor (NET)	Pancreatic neuroendocrine tumor (NET)	G1 G2 G3	PanNET G1 PanNET G2 PanNET G3
		Neuroendocrine carcinoma (NEC)	Pancreatic NEC, small cell-type		Small cell NE carcinoma
		Neuroendocrine carcinoma (NEC)	Pancreatic NEC, large cell-type		Large cell NE carcinoma

NEC are regarded as high grade, but as they represent a separate tumor family, there is no need to for formal grading.
^aThe category of G3 atypical carcinoid in the lung is not a validated entity and not recognized in the 2015 WHO classification. Currently such tumors are classified as small cell lung carcinoma (SCLC) or large cell neuroendocrine carcinoma (LCNEC). High-grade NET with features of atypical carcinoid similar to the G3 tumors of the pancreatic/gastrointestinal tract are rare in the lung, not well characterized and need further study.
^bNot recommended as small cell lung carcinoma (SCLC) is too well ingrained in clinical practice and some SCLC lack commonly used neuroendocrine markers.

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