Which layers of the stomach wall are infiltrated in early gastric carcinoma?

Early Gastric Carcinoma: Definition Based on Depth of Invasion

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

Depth of Invasion in Early Gastric Carcinoma

• Early gastric cancer is specifically defined as a tumor that has invaded only the mucosa (M) or submucosa (SM), corresponding to T1 in the TNM classification system 1
• This definition applies regardless of the lymph node status - even if lymph node metastasis is present, it is still classified as early gastric cancer if confined to these layers 1
• In the TNM classification system, this is further subdivided into:
  • T1a: Tumor confined to the mucosa (M) 1
  • T1b: Tumor confined to the submucosa (SM) 1

Detailed Classification of Submucosal Invasion

• Submucosal invasion can be further classified based on depth:
  • SM1 or T1b1: Tumor invasion is within 0.5 mm of the muscularis mucosae 1
  • SM2 or T1b2: Tumor invasion is 0.5 mm or more deep into the muscularis mucosae 1
• This subclassification is clinically important as deeper submucosal invasion is associated with worse prognosis 1

Distinction from Advanced Gastric Cancer

• Advanced gastric cancer is defined as a tumor which has invaded the muscularis propria (MP) or deeper layers of the gastric wall 1
• Tumors invading the muscularis propria are classified as T2 in the TNM system 1
• The transition from early to advanced gastric cancer occurs when the tumor penetrates beyond the submucosa into the muscularis propria 1

Clinical Significance of Early Gastric Cancer Definition

• The distinction between early and advanced gastric cancer is critical for treatment planning:
  • Early gastric cancers may be amenable to endoscopic resection in select cases 1
  • The risk of lymph node metastasis increases significantly with deeper invasion 1
• Prognosis is significantly better for early gastric cancer compared to advanced disease 2
• Studies have shown that patients with tumors invading the deeper submucosal layer have significantly worse prognoses than those with tumors invading only the superficial submucosal layer 1

Imaging and Diagnostic Considerations

• Multidetector CT criteria for T1a (mucosal) cancer: Tumor shows enhancement and/or thickening of the inner mucosal layer with an intact low-density stripe 1
• Multidetector CT criteria for T1b (submucosal) cancer: Disruption of the low-density stripe layer (less than 50% of the thickness) is visualized 1
• Endoscopic ultrasonography is more accurate for assessing the depth of wall invasion in early cancer 3

In conclusion, early gastric carcinoma is defined by invasion limited to the mucosa and submucosa (T1a and T1b), regardless of lymph node status. This definition is universally accepted across major gastric cancer classification systems, including the Japanese, Chinese, and American guidelines.