Grading according to WHO
G1 highly differentiated
G2 moderately differentiated
G3 badly differentiated

TNM-Classification
TX Primary tumor can not be evaluated
T0 Primary tumor not identifiable
Tis Carcinoma in situ (no infiltration of lamina propria)
T1 Infiltration of lamina propria or submucosa (Early carcinoma can show lymph node metastases)
T2 Infiltration of muscularis propria or subserosa
T3 Penetration of serosa, no infiltration of surrounding structures
T4 Exceedance of organic borders and infiltration of surrounding structures

NX Evaluation of regional lymph nodes is not possible
N0 No regional lymph nodes enlargement
N1 Regional (perigastric) infestation of 1-6 lymph nodes
N2 Regional (perigastric) infestation of 7-15 lymph nodes
N3 Regional (perigastric) infestation of >15 lymph nodes

MX Metastases can not be evaluated
M0 No metastases
M1 Metastases

Staging
Stage 0 Tis N0 M0
Stage Ia T1 N0 M0
Stage Ib T2 N0 M0 or T1 N1 M0
Stage II T1 N2 M0 or T2 N1 M0 or T3 N0 M0
Stage III bad local finding, M0
Stage IV bad local finding, M1

Histological Forms
95% adenocarcinomas (papillary, tubular or mucinous), intestinal type (coherent cellular strands which build tubulus-like structures) and diffuse type (rare, diffusely infiltrating stomach wall),
4% rare forms: Signet ring cell carcinomas, adenosquamous carcinomas, squamous epithelium carcinomas, undifferentiated carcinomas

Endoscopic-macroscopic forms
Type I (bulged), Type II (flat), Type III (excavated)

Localisation
30% Antrum
20% Corpus
40% Fundus (Type-A-gastritis is a precancerous condition)
10% diffuse in whole stomach