How is stomach cancer staged?

by Specialist

An important component of the diagnosis of gastric cancer is staging, and determining the stage plays an important role in determining the treatment of the disease and understanding the outcome. Although all are based on the basic constructs of depth of tumor infiltration (T), degree of lymph node metastasis (N), and degree of distant metastasis (M), in the past the Japanese Gastric Cancer Association (JGCA), the American Cancer Consortium (AJCC), and the International Union Against Cancer (UICC) all had their own staging systems. In recent years, the above three organizations have gradually unified in terms of staging, and a unified TNM staging system has been formed. Currently, doctors in China also follow this system to determine the staging of gastric cancer stages 0 to IV according to different combinations of T, N, and M.

How T, N, and M are determined

First, the structure of the stomach should be described. Usually, the structure of the gastric cavity from the inside to the outside is the mucosal layer, submucosal layer, lamina propria, and plasma layer, and the lymph nodes surrounding the stomach are distributed outside the cavity. According to the different layers of gastric cancer infiltrating the stomach wall, T can be classified as follows:

Tis: the tumor is present only in the epithelial cells of the innermost layer of the gastric wall

T1: the tumor is confined to the mucosa or submucosa

T2: tumor infiltration beyond the submucosa, but confined to the lamina propria

T3: Tumor infiltration beyond the intrinsic muscular layer but confined to the subplasma tissue

T4a: Tumor invades the plasma membrane

T4b: tumor invades adjacent tissue structures

According to the number of lymph nodes where metastasis occurs, N can be classified as follows:

N0: No metastasis in regional lymph nodes
N0: No metastasis in regional lymph nodes

N1: 1 to 2 regional lymph node metastases

N2: 3~6 regional lymph node metastases

N3a: 7~15 regional lymph node metastases

N3b: 16 or more regional lymph node metastases

M can be classified as M0 (no distant metastases) and M1 (distant metastases) based on the presence or absence of distant metastases.

Pathological staging

The gold standard for gastric cancer staging is pathologic staging (pTNM), which is staging based on pathologic evidence. Pathologic staging is generally performed by a pathologist after a patient has undergone radical surgery on a surgically resected specimen to determine T and N, with M taken into account. Among them, distant metastases are usually difficult to determine by pathological examination, and the judgment is often made based on clinical evidence and imaging evidence. If the presence of distant metastases can be confirmed by puncture biopsy, laparoscopic biopsy, or cytology of the abdominal washout fluid, the physician will make a direct judgment of M1, which is determined to be stage IV gastric cancer.

Table 1 Pathological staging (pTNM)
T staging	N Staging	M Staging	Pathologic Staging
Tis	N0	M0	0
T1	N0	M0	ⅠA
T1	N1	M0	ⅠB
T2	N0	M0	ⅠB
T1	N2	M0	IIA
T2	N1	M0	IIA
T3	N0	M0	IIA
T1	N3a	M0	IIB
T2	N2	M0	IIB
T3	N1	M0	IIB
T4a	N0	M0	IIB
T2	N3a	M0	IIIA
T3	N2	M0	IIIA
T4a	N1	M0	IIIA
T4a	N2	M0	IIIA
T4b	N0	M0	IIIA
T1	N3b	M0	IIIB
T2	N3b	M0	IIIB
T3	N3a	M0	IIIB
T4a	N3a	M0	IIIB
T4b	N1	M0	IIIB
T4b	N2	M0	IIIB
T3	N3b	M0	IIIC
T4a	N3b	M0	IIIC
T4b	N3a	M0	IIIC
T4b	N3b	M0	IIIC
Any T	Any N	M1	IV

Table 2 Eighth Edition American Joint Committee on Cancer (AJCC) pTNM Staging

N3a

N3b

ⅠA

ⅠB

IIA

IIB

IIIB

ⅠB

IIA

IIB

IIIA

IIIB

IIA

IIB

IIIA

IIIB

IIIC

T4a

IIB

IIIA

IIIB

IIIC

T4b

IIIA

IIIB

IIIC

Clinical staging

Doctors also often perform clinical staging (cTNM) of gastric cancer, which refers to staging without pathologic evidence, usually by CT, ultrasound endoscopy (EUS), and other methods. This staging has a “niche” and is usually used for initial diagnosis and as a reference for physicians to make initial treatment decisions. Due to the limited accuracy of CT, EUS, etc., cTNM is not as detailed as pTNM. Once the patient has undergone surgery for pathology and obtained pTNM staging, the “mission” of cTNM staging is essentially accomplished, and subsequent treatment decisions and outcome assessment of gastric cancer are based on pTNM staging.

Table 3 Clinical staging (cTNM)
T-staging	N Staging	M Staging	Clinical Staging
Tis	N0	M0	0
T1	N0	M0	I
T2	N0	M0	I
T1	N1,N2 or N3	M0	IIA
T2	N1,N2 or N3	M0	IIA
T3	N0	M0	IIB
T4a	N0	M0	IIB
T3	N1,N2 or N3	M0	III
T4a	N1,N2 or N3	M0	III
T4b	Any N	M0	IVA
Any T	Any N	M1	IVB

Post-neoadjuvant staging

There is also a ypTNM staging that focuses on gastric cancer after preoperative neoadjuvant therapy, with the same basic principles as pTNM staging.

In addition, the eighth edition of TNM staging has new recommendations for gastroesophageal junction cancers, with cancers involving the gastroesophageal junction with a tumor center within 2 cm below the cardia (Siewert type I/II) staged as esophageal cancer and cancers with a tumor center more than 2 cm below the gastroesophageal junction still staged using the TNM staging for gastric cancer.

Staging is an important part of the diagnosis and treatment of gastric cancer, and physicians will refer to these criteria to make a determination. Knowing the stage of the disease also helps patients “know what to expect” when it comes to treatment options and outcomes. (Contributed by Peng Gao, Department of Gastrointestinal Oncology, The First Hospital of China Medical University)