Gastric cancer starts in the lining of the stomach and grows inward

Gastric cancer (also called stomach cancer) begins when malignant cells form in the inner lining of the stomach. The cancer usually develops slowly over years, often without obvious symptoms in its early stages. By the time symptoms appear—such as persistent stomach pain, difficulty swallowing, or unexplained weight loss—the cancer has often spread beyond the stomach lining to deeper layers or to nearby organs and lymph nodes.

The stomach is a muscular organ that holds and breaks down food. Its lining, called the mucosa, is where gastric cancer almost always begins. From there, cancer cells can grow through the stomach wall and into surrounding tissues. The cancer may also spread to distant parts of the body through the bloodstream or lymphatic system, a process called metastasis.

Gastric cancer is less common in the United States than in some other parts of the world, particularly East Asia and parts of Eastern Europe. In the U.S., about 1 in 100 cancers diagnosed is gastric cancer. However, it tends to be diagnosed at a later stage than some other cancers, which affects treatment options and outcomes.

Key Takeaways

  • Gastric cancer develops in the stomach lining and often grows without noticeable symptoms in early stages.
  • The cancer can spread through the stomach wall into deeper layers and to nearby organs, lymph nodes, and distant parts of the body.
  • Certain factors increase risk, including infection with H. pylori bacteria, smoking, heavy alcohol use, obesity, and a family history of gastric cancer.
  • Diagnosis typically involves endoscopy (a camera inserted down the throat) and biopsy to confirm the presence of cancer cells.
  • Treatment options include surgery, chemotherapy, radiation, or combinations of these, depending on the cancer's stage and location.

How gastric cancer develops and spreads

Gastric cancer develops when cells in the stomach lining begin to grow abnormally and multiply without control. This process usually takes years. The cancer typically starts as a precancerous condition—such as chronic inflammation from H. pylori infection or intestinal metaplasia (a change in the stomach lining cells)—before becoming invasive cancer.

Once cancer cells form, they can invade deeper layers of the stomach wall. Doctors describe this progression using stages: Stage 1 means the cancer is confined to the inner lining or has invaded slightly deeper; Stage 2 means it has grown further into the wall; Stage 3 means it has reached nearby lymph nodes or organs; and Stage 4 means it has spread to distant sites like the liver, lungs, or peritoneum (the lining of the abdominal cavity).

The location of the cancer within the stomach matters. Cancers near the junction between the stomach and esophagus (the tube carrying food to the stomach) may cause difficulty swallowing. Cancers in the lower stomach near the small intestine may cause obstruction. Cancers that spread to the peritoneum can cause fluid buildup in the abdomen.

Risk factors that increase the chance of developing gastric cancer

H. pylori infection is the strongest known risk factor. This bacterium lives in the stomach lining and can cause chronic inflammation. People infected with H. pylori have a significantly higher risk of developing gastric cancer, though most infected people never develop cancer. The infection is more common in developing countries and in certain populations.

Other established risk factors include smoking, heavy alcohol consumption, obesity, and a diet high in salt and processed meats. A family history of gastric cancer also raises risk, particularly if a close relative was diagnosed before age 50. Certain genetic syndromes, such as hereditary diffuse gastric cancer (caused by mutations in the CDH1 gene), carry very high risk.

Chronic stomach conditions can increase risk as well. These include pernicious anemia (a condition affecting vitamin B12 absorption), previous stomach surgery, and chronic gastritis (long-term inflammation of the stomach lining). Age is also a factor—gastric cancer is more common in people over 60, though it can occur at any age.

Types of gastric cancer based on cell appearance

The most common type of gastric cancer is adenocarcinoma, which accounts for about 90 percent of cases. Adenocarcinoma develops from mucus-secreting glands in the stomach lining. Doctors further classify adenocarcinomas as either intestinal type (which tends to be associated with H. pylori infection and dietary factors) or diffuse type (which is less common but often more aggressive and may be hereditary).

Other less common types include squamous cell carcinoma (which develops from the flat cells lining the stomach), small cell carcinoma (which behaves aggressively and spreads quickly), and gastrointestinal stromal tumors (which develop from connective tissue cells rather than the lining). The type of cancer affects treatment decisions and prognosis.

Symptoms that may appear as cancer advances

Early gastric cancer often causes no symptoms, which is why it is frequently discovered at a later stage. As the cancer grows, symptoms may include persistent indigestion or heartburn, stomach pain or discomfort, difficulty swallowing, feeling full quickly when eating, nausea, vomiting (sometimes with blood), and unexplained weight loss.

Symptoms depend partly on the cancer's location and size. A cancer blocking the passage between the stomach and small intestine may cause vomiting and inability to keep food down. A cancer eroding blood vessels may cause vomiting of blood or black, tarry stools. Spread to the peritoneum may cause abdominal swelling and fluid accumulation. These symptoms can also result from non-cancerous conditions, so medical evaluation is necessary to determine the cause.

How doctors diagnose gastric cancer

Diagnosis begins with a medical history and physical examination, followed by upper endoscopy, the primary diagnostic tool. During this procedure, a doctor passes a thin, flexible tube with a camera (endoscope) down the throat into the stomach. This allows direct visualization of the stomach lining and any abnormal areas.

If abnormal tissue is seen, the doctor takes a biopsy—small tissue samples that are examined under a microscope to confirm whether cancer cells are present and to determine the cancer type. Once cancer is confirmed, additional imaging tests such as CT scans, ultrasound, or PET scans help determine how far the cancer has spread. Blood tests may also be performed to assess overall health and organ function before treatment.

Treatment approaches based on cancer stage and location

Surgery is the primary treatment when the cancer can be removed. The extent of surgery depends on the cancer's location and stage. A partial gastrectomy removes the affected portion of the stomach; a total gastrectomy removes the entire stomach. The surgeon also removes nearby lymph nodes to check for cancer spread. For early-stage cancers confined to the lining, endoscopic removal (removing the cancer through the endoscope) may be possible without major surgery.

Chemotherapy uses drugs to kill cancer cells throughout the body. It may be given before surgery to shrink the tumor, after surgery to destroy remaining cells, or as the main treatment if surgery is not possible. Radiation therapy uses high-energy beams to target cancer cells and is sometimes combined with chemotherapy. Newer treatments, such as immunotherapy (which helps the immune system recognize and attack cancer cells), are being studied and may be used in certain cases.

Treatment decisions depend on the cancer's stage, the patient's overall health, and whether the goal is cure (for earlier-stage cancers) or symptom management and life extension (for advanced cancers). A multidisciplinary team—including a surgeon, oncologist, and gastroenterologist—typically works together to develop a treatment plan.

Frequently Asked Questions

Is gastric cancer hereditary?

Most gastric cancers are not inherited, but hereditary forms do exist. Hereditary diffuse gastric cancer, caused by CDH1 gene mutations, runs in families and carries a very high lifetime risk. People with a strong family history of gastric cancer (particularly relatives diagnosed young) should discuss genetic testing with their doctor.

Can H. pylori infection be treated to prevent gastric cancer?

Yes. H. pylori can be treated with antibiotics and acid-reducing medications. Treatment eliminates the infection and reduces gastric cancer risk, though the risk does not return to zero. People with H. pylori infection should discuss testing and treatment with their doctor, especially if they have risk factors or family history.

What is the survival rate for gastric cancer?

Survival rates vary widely depending on the cancer's stage at diagnosis. Cancers found early (confined to the stomach lining) have much better outcomes than those found after spreading. Overall five-year survival rates in the U.S. are lower than in countries with screening programs, because cancers are often diagnosed at later stages here.

Can gastric cancer be prevented?

Complete prevention is not possible, but risk can be reduced by treating H. pylori infection, not smoking, limiting alcohol, maintaining a healthy weight, and eating a diet rich in fruits and vegetables. In countries with high gastric cancer rates, screening programs detect cancers earlier, improving outcomes.