Table 1.

TNM Staging Neuroendocrine Tumors of the Colon and Rectum

Primary tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor
T1	Tumor invades lamina propria or submucosa; size <2 cm
T1a	Tumor size <1 cm
T1b	Tumor size 1−2 cm
T2	Tumor invades muscularis propria or size >2 cm with invasion of lamina propria or submucosa
T3	Tumor invades through the muscularis propria into the subserosal tissue without penetration of overlying serosa
T4	Tumor invades peritoneum or other organs
Regional lymph nodes (N)
NX	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Regional lymph node metastasis
Distant metastases (M)
M0	No distant metastasis
M1	Distant metastasis
Anatomic Stage
Stage 0	Tis	N0	M0
Stage I	T1	N0	M0
Stage IIA	T2	N0	M0
Stage IIB	T3	N0	M0
Stage IIIA	T4	N0	M0
Stage IIIB	Any T	N1	M0
Stage IV	Any T	Any N	M1

TNM, tumor, node, metastasis.

Adapted from American Joint Committee on Cancer (AJCC) Cancer Staging Manual. 8th ed. [11].