Which gastric layers, when infiltrated, are considered early gastric carcinoma?

Definition of Early Gastric Carcinoma

Early gastric carcinoma is defined as gastric cancer confined to the mucosa and submucosa, regardless of whether there is evidence of regional lymph node metastasis. 1

Anatomical Classification of Gastric Wall Invasion

Gastric cancer is classified according to the depth of invasion into the gastric wall layers:

• T1 (Early Gastric Cancer):

  • T1a: Tumor confined to the mucosa (M)
  • T1b: Tumor confined to the submucosa (SM)
    • Can be further subclassified as SM1 (invasion within 0.5 mm of the muscularis mucosae) or SM2 (invasion 0.5 mm or more deep into the muscularis mucosae) 1

• T2: Tumor invades the muscularis propria

• T3: Tumor invades the subserosa

• T4a: Tumor penetrates the serosa

• T4b: Tumor invades adjacent structures 1

Significance of Early Gastric Cancer Classification

The distinction between early and advanced gastric cancer is critical because:

1. Prognosis: Early gastric cancer has a significantly better prognosis compared to advanced disease
2. Treatment options: Early gastric cancer may be amenable to endoscopic resection techniques such as EMR or ESD 1
3. Risk of lymph node metastasis: The risk of lymph node metastasis increases with deeper invasion 1

Risk of Lymph Node Metastasis in Early Gastric Cancer

The risk of lymph node metastasis varies based on invasion depth:

• Mucosal cancer: Lower risk of lymph node metastasis
• Submucosal cancer: Higher risk, especially with SM2 invasion 1

Studies have shown that none of the well or moderately differentiated adenocarcinomas measuring <30 mm, with submucosal invasion of <500 μm (Sm1), and without lymphovascular invasion showed lymph node metastasis 1.

Clinical Implications

Understanding the depth of invasion is crucial for determining appropriate treatment:

• Endoscopic resection: May be considered curative for selected early gastric cancers with minimal risk of lymph node metastasis 1
• Surgical resection: Recommended for cases with higher risk of lymph node metastasis or deeper invasion 1

Answer to the Question

Based on the guidelines, option A. Mucosa & submucosa is the correct answer for what constitutes early gastric carcinoma. This is clearly defined in the Chinese Society of Clinical Oncology guidelines which state that "Early-stage gastric cancer is defined as gastric cancer confined to the mucosa and submucosa, regardless of whether there is evidence of regional lymph node metastasis." 1

The other options represent different depths of invasion:

• Option B (Muscularis mucosa): This is part of the mucosal layer and included in T1a
• Option C (Muscularis propria): This represents T2 disease, which is classified as advanced gastric cancer 1
• Option D (Serosa): This represents T4a disease, which is advanced gastric cancer 1