Table 3.

TNM staging for gastrointestinal NET per AJCC 8^th edition ²¹.

T	Primary Tumor	N	Regional lymph nodes
TX	Primary tumor cannot be assessed	Nx	Regional lymph nodes cannot be assessed
T0	No evidence of primary tumor	N0	No regional lymph node metastasis
T1	Invades the lamina propria or submucosa and less than or equal to 1 cm in size	N1	Regional lymph node metastasis
T2	Invades the muscularis propria or greater than 1 cm in size	M	Distant metastasis
T3	Invades through the muscularis propria into subserosal tissue without penetration of overlying serosa	M0	No distant metastasis
T4	Invades visceral peritoneum (serosa) or other organs or adjacent structures	M1	M1a: Metastasis confined to liver M1b: Metastases in at least one extrahepatic site M1c: Both hepatic and extrahepatic metastases