TNM Definitions
AJCC Stage Groupings

The American Joint Committee on Cancer (AJCC) has designated staging by TNM classification.[1-3]

Primary tumor (T)

• TX: Primary tumor cannot be assessed
• T0: No evidence of primary tumor
• Tis: Carcinoma in situ: intraepithelial tumor without invasion of the lamina propria
• T1: Tumor invades lamina propria or submucosa
• T2: Tumor invades the muscularis propria or the subserosa*
  • T2a: Tumor invades muscularis propria
  • T2b: Tumor invades subserosa
• T3: Tumor penetrates the serosa (visceral peritoneum) without invading adjacent structures**^,***
• T4: Tumor invades adjacent structures**^,***

* [Note: A tumor may penetrate the muscularis propria with extension into the gastrocolic or gastrohepatic ligaments, or into the greater or lesser omentum, without perforation of the visceral peritoneum covering these structures. In this case, the tumor is classified T2. If there is perforation of the visceral peritoneum covering the gastric ligaments or the omentum, the tumor should be classified T3.]

** [Note: The adjacent structures of the stomach include the spleen, transverse colon, liver, diaphragm, pancreas, abdominal wall, adrenal gland, kidney, small intestine, and retroperitoneum.]

*** [Note: Intramural extension to the duodenum or esophagus is classified by the depth of greatest invasion in any of these sites, including stomach.]

Regional lymph nodes (N)

The regional lymph nodes are the perigastric nodes, found along the lesser and greater curvatures, and the nodes located along the left gastric, common hepatic, splenic, and celiac arteries. For pN, a regional lymphadenectomy specimen will ordinarily contain at least 15 lymph nodes. Involvement of other intra-abdominal lymph nodes, such as the hepatoduodenal, retropancreatic, mesenteric, and para-aortic, is classified as distant metastasis.

• NX: Regional lymph node(s) cannot be assessed
• N0: No regional lymph node metastasis*
• N1: Metastasis in one to six regional lymph nodes
• N2: Metastasis in 7 to 15 regional lymph nodes
• N3: Metastasis in more than 15 regional lymph nodes

* [Note: A designation of pN0 should be used if all examined lymph nodes are negative, regardless of the total number removed and examined.]

Distant metastasis (M)

• MX: Distant metastasis cannot be assessed
• M0: No distant metastasis
• M1: Distant metastasis

Stage 0

• Tis, N0, M0

Stage IA

• T1, N0, M0

Stage IB

• T1, N1, M0
• T2a, N0, M0
• T2b, N0, M0

Stage II

• T1, N2, M0
• T2a, N1, M0
• T2b, N1, M0
• T3, N0, M0

Stage IIIA

• T2a, N2, M0
• T2b, N2, M0
• T3, N1, M0
• T4, N0, M0

Stage IIIB

• T3, N2, M0

Stage IV

• T4, N1, M0
• T4, N2, M0
• T4, N3, M0
• T1, N3, M0
• T2, N3, M0
• T3, N3, M0
• Any T, any N, M1

References

1. Stomach. In: American Joint Committee on Cancer.: AJCC Cancer Staging Manual. 6th ed. New York, NY: Springer, 2002, pp 99-106. 
   
   
2. Roder JD, Böttcher K, Busch R, et al.: Classification of regional lymph node metastasis from gastric carcinoma. German Gastric Cancer Study Group. Cancer 82 (4): 621-31, 1998.  [PUBMED Abstract]
   
   
3. Ichikura T, Tomimatsu S, Uefuji K, et al.: Evaluation of the New American Joint Committee on Cancer/International Union against cancer classification of lymph node metastasis from gastric carcinoma in comparison with the Japanese classification. Cancer 86 (4): 553-8, 1999.  [PUBMED Abstract]