Stomach cancer is caused by certain changes to the way stomach cells function, especially how they grow and divide into new cells. The exact cause of these changes is unknown, but there are several risk factors that may increase the chance of developing stomach cancer. These risk factors include:

• Helicobacter pylori infection: Chronic infection of the mucosal layer of the stomach with H. pylori is a major risk factor for stomach cancer. This bacterium spreads from person to person through direct contact with saliva, vomit, or stool.

• Age: Stomach cancer can be diagnosed at any age, but the risk increases as a person gets older.

• Diet: A diet high in smoked or salted foods and processed meat and low in vegetables is a risk factor for stomach cancer. On the other hand, some of the foods that might lower stomach cancer risk, such as fruits and vegetables, contain antioxidants that can block substances that damage a cell’s DNA.

• Tobacco use: Smoking tobacco doubles the risk of stomach cancer.

• Family history: A family history of stomach cancer increases the risk of developing the disease.

• Obesity: Obesity increases the risk of cancer in the upper stomach.

• Gastroesophageal reflux disease (GERD): GERD increases the risk of cancer in the upper stomach.

• Pernicious anemia: Pernicious anemia, a type of anemia caused by vitamin B12 deficiency, increases the risk of stomach cancer.

• Previous stomach surgery: Partial gastrectomy for ulcer disease after about 20 years increases the risk of stomach cancer.

• Blood type: Stomach cancer is more common in people with Type A blood.

• Certain genetic conditions: Several genetic conditions are associated with increased gastric cancer risk.

It is important to note that not everyone with these risk factors gets stomach cancer, and stomach cancer can still occur in the absence of any of these factors or conditions.