Table 3.

The 8th edition of the American Joint Commission on Cancer (AJCC) staging system for NET of the appendix [22] and differences in staging: ENET guidelines [24].

The 8th edition of the AJCC staging system for NET of the appendix [22]		Differences in staging: ENET guidelines [24]
T—primary tumor
T0	There is no indication or evidence of a primary tumor.
T1	The tumor measures 2 cm or less in its largest dimension.
T2	The tumor measures more than 2 cm but is less than or equal to 4 cm in its greatest dimension.	The tumor, with a size of ≤2 cm, exhibits infiltration into the submucosa and the muscularis propria and/or minimal (≤3 mm) infiltration of the subserosa and/or mesoappendix.
T3	The tumor measures more than 4 cm or displays subserosal invasion or involvement of the mesoappendix.	The tumor is greater than 2 cm and/or demonstrates extensive (>3 mm) infiltration of the subserosa and/or mesoappendix.
T4	The tumor perforates the peritoneum or directly invades other adjacent organs or structures, excluding direct mural extension to the adjacent subserosa of the adjacent bowel (e.g., abdominal wall and skeletal muscle).	The tumor exhibits infiltration of the peritoneum and/or another adjacent organ.
N
Nx	Regional lymph nodes cannot be assessed.
N0	No regional lymph node metastasis
N1	No regional lymph node metastasis
M
M1	Distant metastasis
M1a	Liver metastasis
M1b	At least one extrahepatic site of metastasis (e.g., lung, ovary, nonregional lymph node, peritoneum, bone)
M1c	Both hepatic and extrahepatic metastases