- Peak incidence: 70 years- High incidence in South Korea and Japan

Etiology: - Diet rich in nitrates and/or salts (e.g., dried, preserved food) - Alcohol and nicotine use- Low socioeconomic status- Atrophic gastritis- H. pylori infection: associated with a higher risk of intestinal gastric cancer but not with diffuse gastric cancer- Gastric ulcers- Partial gastrectomy- Adenomatous gastric polyps- Hereditary factors (positive family history, hereditary non‑polyposis colorectal cancer)- Higher incidence in individuals with blood type A

Clinical features:- Weight loss, iron deficience anemia- Abdominal pain- Early satiety- Nausea or vomiting- Acute gastric bleeding (hematemesis, melena)- Later: Gastric outlet obstruction, Virchow's nodule, Sister Mary Joseph's nodule, acanthosis nigricans

Pathology:- Adenocarcinoma (90% of cases):→ Typically localized, exophytic lesion +/- ulceration→ Arise from glandular cells in the stomach; usually located on the lesser curvature of the stomach- Signet ring cell carcinoma→ Diffuse growth→ Round cells filled with mucin, with a flat nucleus in the cell periphery- Adenosquamous carcinoma- Squamous cell carcinoma- Other: MALT lymphoma, sarcoma, gastrointestinal stromal tumor (GIST), carcinoid

Lauren classification of gastric adenocarcinoma:- Intestinal type (∼50% of cases): polypoid, glandular formation; cells look like intestinal cells; expanding (not infiltrative) growth pattern; clear border - Diffuse type (∼40% of cases): infiltrative growth and diffuse spread in the gastric wall; cells secrete mucous; no clear border → larger safety margin- Mixed type (∼10% of cases)

Differential diagnosis: Gastric ulcer, GERD, Ménétrier's disease

Treatment:- Endoscopic resection- Surgery: Roux-en-Y gastric bypass- Perioperative chemotherapy, sometimes radiotherapy- Trastuzumab is indicated for HER2+ gastric adenocarcinomas