What is the recommended staging classification for gastric cancer?

Recommended Staging Classification for Gastric Cancer

The TNM staging system according to the AJCC/UICC classification (currently 8th edition) is the recommended staging system for gastric cancer, requiring evaluation of at least 16 lymph nodes for adequate pathological staging. 1

Primary Staging System

The TNM classification system jointly developed by the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC) is the standard staging system used in Western countries and increasingly adopted worldwide. 1 This system has undergone harmonization with the Japanese Classification of Gastric Carcinoma to create consistent T and N categories internationally. 2

Key TNM Components

Tumor (T) Classification:

• Tis: Carcinoma in situ (intraepithelial tumor without invasion of lamina propria) 1
• T1: Tumor invades lamina propria or submucosa 1
  • T1a: invasion of lamina propria or muscularis mucosae 1
  • T1b: invasion into submucosa 1
• T2: Tumor invades muscularis propria 1
• T3: Tumor penetrates subserosal connective tissue without invasion of visceral peritoneum 1
• T4: Tumor invades serosa or adjacent structures 1
  • T4a: tumor invades serosa (visceral peritoneum) 1
  • T4b: tumor invades adjacent structures 1

Nodal (N) Classification:

• N0: No regional lymph node metastasis 1
• N1: Metastasis in 1-6 regional lymph nodes 1
• N2: Metastasis in 7-15 regional lymph nodes 1
• N3: Metastasis in >15 regional lymph nodes 1

Metastasis (M) Classification:

• M0: No distant metastasis 1
• M1: Distant metastasis present 1

Critical Staging Requirements

A minimum of 16 lymph nodes must be pathologically evaluated to avoid staging inaccuracy, with >30 lymph nodes preferred for optimal accuracy. 1 The ESMO guidelines recommend that at least 14 lymph nodes, and optimally 25 or more, should be recovered during surgical resection. 1, 3

Lymph Node Documentation

Surgeons and pathologists should collect and group perigastric lymph nodes according to their respective stations, documenting both the total number of metastatic lymph nodes and the station-specific involvement (e.g., "Lymph node station no. χ: number of metastatic lymph nodes/number of examined lymph nodes"). 1

Special Anatomic Considerations

For tumors at the esophagogastric junction (EGJ), the staging system depends on tumor epicenter location: 1

• If the tumor epicenter is within 2 cm from the EGJ: use esophageal cancer staging criteria 1
• If the tumor epicenter is >2 cm from the EGJ: use gastric cancer staging criteria 1

This distinction remains somewhat controversial, as Chinese data suggest EGJ carcinomas (Siewert II) may have greater biological similarity to gastric cancer than esophageal cancer, though larger validation studies are needed. 1

Clinical vs. Pathological Staging

Both clinical (cTNM) and pathological (pTNM) staging should be documented. 1 Clinical staging guides initial treatment planning, while pathological staging provides definitive prognostic information and guides adjuvant therapy decisions. 3

Clinical Staging Modalities

The comprehensive staging workup should include: 1, 3

• Physical examination, blood count, liver and renal function tests
• Endoscopy with biopsy
• CT scan of thorax, abdomen, and pelvis (with contrast enhancement)
• Endoscopic ultrasound (EUS) for T staging (sensitivity 0.86, specificity 0.90 for distinguishing T1/2 from T3/4) 1
• Laparoscopy with peritoneal washings for potentially resectable cases 1
• PET-CT may upstage patients but can be negative in mucinous and diffuse tumors 1

Pathological Reporting Requirements

The pathological report must include: 1

• Tumor site and size
• Histological subtype (Lauren classification: intestinal, diffuse, or mixed type) 1
• Histological grade (G1, G2, G3)
• Depth of infiltration (pT stage)
• Number of lymph node metastases/total lymph nodes examined (pN stage)
• Vascular, lymphatic, and nerve invasion
• Surgical margin status (positive if cancer cells within 1 mm of resected margin) 1
• Distant metastasis status (pM stage)
• HER2 expression status for all adenocarcinomas 1

Additional Pathological Nuances

For T2 tumors (muscularis propria invasion), specify whether invasion is superficial or deep, as this impacts prognosis and treatment planning. 1 Carcinomatous nodules in subserosal adipose tissue should be counted as regional lymph node metastases even without residual lymph node tissue. 1

Common Pitfalls to Avoid

• Inadequate lymph node harvest: Fewer than 16 examined lymph nodes leads to stage migration and inaccurate prognostication 1
• Misclassification of EGJ tumors: Carefully measure tumor epicenter distance from the EGJ 1
• Overlooking peritoneal metastases: Laparoscopy with washings is essential for detecting occult M1 disease 1
• Incomplete pathological reporting: Ensure all required elements are documented, including HER2 status 1