Characteristics and long-term prognosis of patients with rectal neuroendocrine tumors

Table 1 Proposed tumor-node-metastasis classification for neuroendocrine tumors of the rectum (European Neuroendocrine Tumor Society 2007)[7]

TNM classification
T: Primary tumor
Tx	Primary tumor cannot be assessed
T0	No evidence of primary tumor
T1	Tumor invades the mucosa or submucosa and size ≤ 1 cm
	T1a: size < 1 cm
	T1b: size 1-2 cm
T2	Tumor invades the muscularis propria or size > 2 cm
T3	Tumor invades subserosa/pericolic/perirectal fat
T4	Tumor directly invades other organs/structures and/or perforates the visceral peritoneum
N: Regional lymph nodes
Nx	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Regional lymph node metastasis
M: Distant metastasis
MX	Distant metastasis cannot be assessed
M0	No distant metastases
M1	Distant metastasis

TNM: Tumor-node-metastasis.