What are the classification criteria for early gastric cancer, including depth of invasion, macroscopic appearance, and histologic differentiation?

Early Gastric Cancer Classification

Early gastric cancer (EGC) is defined as adenocarcinoma confined to the mucosa (T1a) or submucosa (T1b), regardless of lymph node metastasis status. 1

Depth of Invasion Classification

The depth of tumor invasion follows the T-category system with specific anatomical boundaries 1:

• T1a (Mucosal): Tumor confined to the mucosa (M), including invasion into the muscularis mucosae 1
• T1b (Submucosal): Tumor confined to the submucosa (SM) 1
  • SM1 (T1b1): Invasion within 0.5 mm of the muscularis mucosae 1
  • SM2 (T1b2): Invasion 0.5 mm or more deep into the submucosa 1
• T2 and beyond: Tumor invading the muscularis propria or deeper—this is no longer classified as early gastric cancer 1

Critical distinction: The prefix "p" (pathological) or "c" (clinical) is used with T-category notation (e.g., pT1a), not with the anatomical descriptors M or SM 1.

Macroscopic Appearance Classification

EGC is classified as Type 0 (superficial) and further subdivided into six distinct patterns 1:

Type 0 Subclassification

• Type 0-I (Protruding): Polypoid tumors with >3mm elevation 1
• Type 0-IIa (Superficial Elevated): Slightly elevated tumors with ≤3mm elevation 1
• Type 0-IIb (Superficial Flat): Tumors without elevation or depression 1
• Type 0-IIc (Superficial Depressed): Slightly depressed tumors 1
• Type 0-III (Excavated): Tumors with deep depression 1

For mixed morphology: Record all components in descending order of surface area occupied (e.g., 0-IIc + III) 1. The elevated type (0-I, 0-IIa) is strongly predictive of differentiated histology with a positive likelihood ratio of 15.7 2.

Histologic Differentiation

Differentiated-Type Carcinoma 1

Includes:

• Papillary adenocarcinoma (pap)
• Tubular adenocarcinoma (tub1, tub2)

Undifferentiated-Type Carcinoma 1

Includes:

• Poorly differentiated adenocarcinoma (por1, por2)
• Signet-ring cell carcinoma (sig)

Special consideration: Mucinous adenocarcinoma (muc) found in the submucosal layer is classified as non-curative regardless of its origin from differentiated or undifferentiated type 1.

For mixed histology: Record all histological types in descending order of quantitative predominance (e.g., tub2 > tub1), but classify the tumor according to the predominant component 1.

Clinical Predictors and Risk Stratification

Lymph Node Metastasis Risk 3, 4

• Mucosal tumors (T1a): 2.3-3.4% overall risk 3, 4

  • Without ulceration: Essentially 0% risk—all mucosal tumors with lymph node metastasis had ulceration 4
  • With ulceration: All cases of nodal involvement occurred in this subset 4

• Submucosal tumors (T1b): 19.8-21.7% overall risk 3, 4

  • SM1a (<200 μm invasion): Significantly lower risk, metastases confined to N1 (epigastric) nodes 4
  • SM2 (≥200 μm invasion): Higher risk of nodal involvement 4

• Elevated type lesions: 20.9% nodal metastasis rate 3

Prognostic Factors

Favorable indicators 2, 4:

• Older age (≥72 years) correlates with differentiated type 2
• Male sex associated with differentiated type 2
• Larger tumor size (>30 mm) predicts differentiated type 2
• Elevated macroscopic type strongly predicts differentiated histology 2

Unfavorable indicators 5, 6:

• Papillary adenocarcinoma has worse prognosis than tubular adenocarcinoma due to deeper penetration and more lymphovascular invasion 5
• Lymph node invasion and invasion through muscularis mucosae are independent poor prognostic factors 6

Common Pitfalls

Ulceration assessment: Diagnosis of ulceration (UL) should be based primarily on histological evidence, but endoscopic and radiological findings must be considered when making the conclusive diagnosis 1. Biopsy-derived scars showing fibrosis just beneath the muscularis mucosae should be classified as UL(+) if they cannot be discriminated from true ulcer scars 1.

Signet ring cell carcinoma misconception: Contrary to common belief, intramucosal signet ring cell carcinoma demonstrates low risk of nodal metastasis, comparable to early intestinal-type EGC 5.