According to the Japanese classification, which depth of gastric cancer invasion is defined as invasion limited to the mucosa and submucosa, regardless of lymph node involvement?

Explanation

## Early Gastric Cancer Definition **Key Point:** Early gastric cancer (EGC) is defined by the Japanese Gastric Cancer Association as any gastric cancer with invasion limited to the mucosa (M) and submucosa (SM), **regardless of lymph node metastasis status**. This is a depth-based definition, not a stage-based one. ### Japanese Classification Depth Layers | Layer | Abbreviation | Definition | Prognosis | |-------|--------------|------------|----------| | Mucosa | M1, M2, M3 | Epithelium, muscularis mucosae, submucosa | Excellent (5-year survival ~90%) | | Submucosa | SM1, SM2, SM3 | Upper, middle, deep third of submucosa | Good (5-year survival ~80%) | | Muscularis propria | MP | Muscle layer | Fair (5-year survival ~60%) | | Subserosa | SS | Below serosa | Poor (5-year survival ~40%) | | Serosa | SE | Through serosa | Very poor | **High-Yield:** The critical distinction is that **EGC can have lymph node metastases** (up to 3% with M cancers, up to 20% with SM cancers) but is still classified as "early" because the depth is limited. This is fundamentally different from the TNM system, where stage depends on both T and N. ### Clinical Significance - **Endoscopic resection** is curative for mucosal cancers without lymphovascular invasion - **Gastrectomy with D2 lymphadenectomy** is standard for submucosally invasive EGC - **Prognosis is excellent** even with nodal involvement, provided invasion is limited to mucosa/submucosa **Clinical Pearl:** A T1 gastric cancer with N2 disease still has a better prognosis than a T3 N0 cancer, illustrating why the Japanese depth-based classification is prognostically superior to TNM alone in early disease. [cite:Japanese Gastric Cancer Association Classification, Harrison 21e Ch 297]