Pathologic research update of colorectal neuroendocrine tumors

Table 1 Classification of NETs of the colon and rectum[14,15]

Well-differentiated neuroendocrine tumor (carcinoid)

Benign: Non-functioning, confined to mucosa-submucosa, non-angioinvasive, < 1 cm in size (ileum) or ≤ 2 cm colon and rectum

Serotonin-producing tumor

Enteroglucagon-producing tumor

Benign or low-grade malignant (uncertain malignant potential): non-functioning, confined to mucosa-submucosa, angioinvasion, or < 1 cm in size (ileum) or ≤ 2 cm colon and rectum

Serotonin-producing tumor

Enteroglucagon-producing tumor

Well-differentiated neuroendocrine carcinoma (malignant carcinoid)

Low-grade malignant: invasion of the muscularis propria and beyond or metastases

Non-functioning or functioning serotonin-producing carcinoma (with carcinoid syndrome)

Non-functioning enteroglucagon-producing carcinoma

Poorly-differentiated neuroendocrine carcinoma

High-grade malignant

NETs: Neuroendocrine tumors.

Table 2 Proposed staging system for rectal and colon NETs[62,63]

	Rectal	Colon
Depth of invasion and size
T1	Up to and into muscularis propria, ≤ 1 cm	Any depth of invasion, ≤ 1 cm
	Up to muscularis propria, > 1 to ≤ 2 cm	Up to or including muscularis propria, > 1 to ≤ 4 cm
T2	Beyond muscularis propria, ≤ 1 cm	Beyond muscularis propria, > 1 to ≤ 4 cm
	Into muscularis propria, > 1 to ≤ 2 cm	Up to or including muscularis propria, > 4 cm
	Up to and into muscularis propria, > 2 cm
T3	Invasion beyond muscularis propria, > 1 cm	Beyond muscularis propria, > 4 cm
Lymph node
N0	No lymph node metastasis
N1	Regional lymph node metastasis
Distant metastasis
M0	No distant metastasis
M1	Distant metastasis
Stage
I	T1; N0; M0
II	T1; N1; M0 or T2; Any N; M0
III	T3; N0; M0 or T3; N1; M0
IV	Any T; Any N; M1