Early Gastric Adenocarcinoma

Early gastric adenocarcinoma (EGC) is defined as gastric carcinoma confined to mucosa (T1a, intramucosal) or submucosa (T1b) regardless of lymph node involvement, distinct from advanced gastric cancer which extends beyond muscularis propria. Histologically classified using Lauren classification (intestinal type — well-differentiated, glandular, often associated with H. pylori atrophic gastritis; diffuse type — poorly cohesive, signet ring cells, more aggressive, hereditary in CDH1 mutation) or WHO classification (tubular, papillary, mucinous, poorly cohesive). Endoscopic appearance classified by Paris classification: type 0-I protruding (0-Is sessile, 0-Ip pedunculated), 0-IIa elevated (<2.5 mm), 0-IIb flat (entirely flat), 0-IIc depressed (<2.5 mm depression), 0-III excavated.

Epidemiology shows substantial geographic variation: highest incidence in East Asia (Japan, Korea, China — 30-40% of all gastric cancers detected as EGC due to mass screening), intermediate in Eastern Europe, Latin America, lower in Western countries (5-10% of all gastric cancers as EGC due to lack of screening). Risk factors include H. pylori infection (most important — atrophic gastritis, intestinal metaplasia, dysplasia, cancer sequence), pernicious anemia, partial gastrectomy, hereditary diffuse gastric cancer (CDH1, CTNNA1), Lynch syndrome, familial adenomatous polyposis, smoking, dietary factors (high salt, smoked foods, low fruit/vegetables), Epstein-Barr virus association in 10%. Pathogenesis follows Correa cascade for intestinal type (chronic gastritis → atrophy → intestinal metaplasia → dysplasia → carcinoma) over decades.

Diagnosis is by upper endoscopy with high-definition white light, narrow-band imaging, magnification endoscopy, chromoendoscopy with indigo carmine or acetic acid, careful evaluation of lesion characteristics (size, depth, margins, ulceration), targeted biopsies. Endoscopic ultrasound assesses depth of invasion (mucosa, submucosa, muscularis propria) and regional lymph nodes. CT chest/abdomen/pelvis for distant staging. Treatment: endoscopic submucosal dissection (ESD) for absolute indications (mucosal differentiated adenocarcinoma ≤2 cm without ulceration), expanded indications (larger differentiated mucosal lesions, undifferentiated mucosal ≤2 cm, slight submucosal invasion <500 μm) — curative if R0, no lymphovascular invasion, no ulceration in undifferentiated. Surgical gastrectomy (subtotal or total) with D1+ or D2 lymphadenectomy for unsuitable for ESD or non-curative ESD. Adjuvant therapy generally not required for EGC. Surveillance endoscopy every 6-12 months for 5 years post-resection. H. pylori eradication mandatory. Five-year survival: 90%+ overall, near 100% for T1a NO, 85-95% for T1b N0.