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.