Stomach cancer develops when cells in the stomach lining accumulate DNA damage over time, causing them to grow uncontrollably. In most cases, this process takes years or even decades, driven by a combination of chronic infection, lifestyle habits, and genetic factors. About 0.8% of Americans will be diagnosed with stomach cancer at some point in their lifetime, with roughly 31,500 new cases expected in 2026 alone.
The disease rarely has a single cause. Instead, multiple risk factors work together, gradually transforming healthy stomach tissue through a progression of worsening changes: first chronic inflammation, then thinning of the stomach lining, then abnormal cell growth, and finally cancer. Understanding what drives each stage helps clarify why some people develop stomach cancer and others don’t.
H. pylori: The Leading Cause
The bacterium Helicobacter pylori is the single biggest risk factor for stomach cancer, particularly cancers in the lower and middle portions of the stomach. This spiral-shaped bacterium burrows into the mucus layer protecting the stomach lining and triggers chronic inflammation that can persist for decades if untreated. The constant cycle of tissue damage and repair increases the rate at which cells divide, and each division is an opportunity for harmful mutations to accumulate.
Certain strains of H. pylori are more dangerous than others. Some produce a toxin called CagA that gets injected directly into stomach lining cells. Once inside, CagA disables the normal controls on cell growth and makes cells more mobile, two hallmarks of cancer development. Long-term exposure to this toxin sustains chronic inflammation, compounding the damage.
H. pylori infects roughly half the world’s population, though most carriers never develop cancer. The infection spreads through contaminated food, water, or close person-to-person contact, and it’s far more common in countries with limited sanitation. A simple breath test or stool test can detect it, and a course of antibiotics can eliminate it.
How Normal Tissue Becomes Cancerous
Stomach cancer doesn’t appear overnight. In the most common form (intestinal-type adenocarcinoma), the stomach lining passes through a well-documented series of changes. It starts with chronic inflammation of the stomach lining, often from H. pylori. Over years, this progresses to atrophic gastritis, where the acid-producing glands thin out and lose function. Next comes intestinal metaplasia, where stomach cells start to resemble intestinal cells, a sign the tissue is under sustained stress. If abnormal cells continue accumulating mutations, dysplasia develops, meaning cells look increasingly abnormal under a microscope. The final step is full adenocarcinoma.
This entire process can span 20 to 30 years. Not everyone progresses through every stage, and the cascade can be interrupted at any point by treating the underlying cause, particularly H. pylori infection. People diagnosed with atrophic gastritis or intestinal metaplasia are sometimes monitored with periodic endoscopies to catch problems early.
Smoking and Alcohol
Smoking independently raises stomach cancer risk. Current smokers have about a 28% higher risk compared to nonsmokers, while even former smokers carry a roughly 12% increase. The chemicals in tobacco smoke reach the stomach both through swallowed saliva and through the bloodstream, contributing to DNA damage in the stomach lining.
Heavy alcohol use also plays a role. Drinking five or more alcoholic beverages daily has been linked to more than a three-fold increase in the odds of developing stomach cancer. At more moderate levels, the relationship is weaker, with heavy drinkers (four or more drinks daily) showing about a 20% higher risk compared to non-drinkers. The combination of heavy smoking and heavy drinking is particularly dangerous. A Norwegian population study found that people who smoked more than 20 cigarettes a day and drank frequently had five times the risk of non-cardia stomach cancer compared to people who did neither.
Diet and Stomach Cancer Risk
Diets high in salt-preserved, smoked, and pickled foods have long been associated with higher rates of stomach cancer. Salt damages the protective mucus layer of the stomach, making cells more vulnerable to carcinogens and inflammation. This helps explain why stomach cancer rates are historically higher in East Asia, parts of South America, and Eastern Europe, where heavily salted and preserved foods are dietary staples.
The role of nitrates and nitrites, found in processed meats like bacon, hot dogs, and deli meats, is less clear-cut than commonly believed. These compounds can be converted in the stomach into N-nitroso compounds, which damage DNA. However, large prospective studies examining dietary nitrate and nitrite intake have produced inconsistent results, and the overall body of evidence remains inconclusive for a direct link to stomach cancer. That said, the World Health Organization classifies processed meat as a carcinogen based on its association with colorectal cancer, and limiting intake is generally a reasonable choice.
Diets rich in fresh fruits and vegetables appear to be protective. The antioxidants in these foods, particularly vitamin C, may help neutralize harmful compounds in the stomach before they can cause damage.
Obesity and Acid Reflux
Excess body weight and chronic gastroesophageal reflux disease (GERD) are particularly important risk factors for cancers developing in the upper part of the stomach, near where it connects to the esophagus. Together, obesity and GERD account for roughly a third of these upper-stomach cancers. Obesity promotes chronic low-grade inflammation throughout the body and increases abdominal pressure, which worsens reflux. The repeated exposure of upper stomach tissue to acid and bile creates conditions favorable for cancer development.
Genetic and Family Risk
A small percentage of stomach cancers are driven primarily by inherited genetic mutations. The most well-characterized is a mutation in the CDH1 gene, which causes hereditary diffuse gastric cancer. People carrying this mutation face a lifetime risk that ranges from 37% to 70% in men and 25% to 83% in women. Because the risk is so high, carriers are often advised to consider preventive removal of the stomach.
Beyond CDH1, having a first-degree relative (parent, sibling, or child) with stomach cancer roughly doubles or triples your own risk, even without a known gene mutation. This likely reflects a combination of shared genetics, shared H. pylori exposure within households, and similar dietary habits. Certain inherited cancer syndromes, including Lynch syndrome and familial adenomatous polyposis, also carry elevated stomach cancer risk.
Workplace and Environmental Exposures
Several occupational exposures have been linked to higher stomach cancer rates, though these account for a much smaller share of cases than infection or lifestyle factors. Workers with significant exposure to the following materials face elevated risk:
- Asbestos: Workers with high exposure showed roughly 46% higher stomach cancer mortality in pooled analyses.
- Coal dust: Evidence for increased risk among coal miners is strong. Mining dust contains coal, metals, polycyclic aromatic hydrocarbons, and silica.
- Metal dust: Exposure to beryllium, chromium, and nickel was associated with a 50% excess risk in one U.S. study. Lead exposure among battery workers and smelters also raises risk.
- Silica and wood dust: Both have been significantly associated with stomach cancer in large studies.
- Nitrogen compounds: Underground miners exposed to nitrogen oxides from explosives and diesel equipment face additional risk, as these compounds can directly damage DNA.
People who worked with cutting fluids in metalworking or handled certain pesticides may also have been exposed to nitrosamines, potent cancer-causing compounds that have been detected at high concentrations in industrial settings.
Other Risk Factors
Several additional factors raise stomach cancer risk. Men develop the disease about twice as often as women, for reasons that aren’t fully understood but likely involve hormonal differences. Risk increases sharply with age, with most diagnoses occurring after 60. Blood type A is associated with a modestly higher risk, possibly because it affects how the immune system interacts with H. pylori. Previous stomach surgery, particularly procedures that reduce acid production, can also increase long-term risk by changing the stomach’s internal environment.
Pernicious anemia, a condition in which the body can’t absorb vitamin B12 properly due to damage to stomach lining cells, is another recognized risk factor. The same atrophic changes that cause the anemia also set the stage for the precancerous progression described earlier.
Who Gets Stomach Cancer
In the United States, the overall incidence rate is 7.5 new cases per 100,000 people per year. New case rates have been rising about 1.1% annually over the past decade, a trend driven largely by increases among younger adults. Death rates, however, have been falling by about 2% per year, reflecting improvements in treatment and earlier detection in some populations.
Globally, stomach cancer is the fifth most common cancer and remains a leading cause of cancer death, particularly in East Asia, Central and South America, and Eastern Europe. The geographic variation strongly mirrors patterns of H. pylori prevalence, salt-heavy diets, and access to refrigeration (which reduces the need for salt-based food preservation). In countries where screening programs exist, such as South Korea and Japan, cancers tend to be caught at earlier, more treatable stages.