While the exact cause of stomach cancer is unknown, several factors have been found to play a role in its development. These risk factors include:

• A chronic infection by a bacteria called helicobacter pylori
• Gastroesophageal reflux disease
• A diet high in salted or preserved (cured/smoked/pickled) foods
• A diet low in fruits and vegetables
• Smoking and alcohol
• Family history of stomach cancer
• Hereditary syndromes such as familial adenomatous polyposis (FAP), Li-Fraumeni syndrome, hereditary nonpolyposis colorectal cancer (HNPCC) and Peutz-Jeghers syndrome
• Medical conditions that may contribute to stomach cancer such as:
  • Anaemia (megaloblastic anaemia and pernicious anaemia)
  • Previous stomach operation with partial removal of the stomach (gastrectomy)
  • A stomach disorder called atrophic gastritis, which results in lower than normal production of digestive juices
  • Stomach polyps

These risk factors are more commonly seen in people who have stomach cancer. Having one or more of these risk factors does not mean that you will develop stomach cancer. Stomach cancer may still develop in patients with none of the above risk factors.