Stomach cancer, also called gastric cancer, is a growth of abnormal cells that begins in the lining of the stomach. About 90% of all stomach cancers are adenocarcinomas, meaning they start in the gland cells that produce mucus and digestive fluids along the stomach’s inner wall. The cancer typically grows outward through the stomach’s layers over time, and survival depends heavily on how early it’s caught.
Types of Stomach Cancer
The vast majority of stomach cancers are adenocarcinomas. These begin in the innermost layer of the stomach (the mucosa) and gradually invade deeper layers of the stomach wall as they progress. When people refer to “stomach cancer” without further detail, they almost always mean this type.
Less common types include gastrointestinal stromal tumors (GISTs), which develop in specialized cells within the stomach wall that help coordinate muscle contractions for digestion, and carcinoid tumors, which form in the stomach’s hormone-producing cells. These rarer cancers behave differently and are treated differently than adenocarcinomas.
Symptoms
Stomach cancer is notoriously hard to detect early because its symptoms overlap with common, benign digestive problems. You might experience persistent indigestion, heartburn, or a vague stomach pain that doesn’t go away. Feeling bloated after meals, or feeling full after eating only a small amount of food, is another common sign. Nausea, vomiting, difficulty swallowing, and unintentional weight loss can also develop.
Many people dismiss these symptoms for months because they resemble acid reflux or a stomach bug. The key distinction is persistence. Occasional heartburn is normal. Heartburn or stomach discomfort that lasts for weeks, especially combined with unexplained weight loss or a shrinking appetite, warrants a closer look.
What Causes It
The single biggest risk factor for stomach cancer is chronic infection with a bacterium called Helicobacter pylori (H. pylori). This common infection, which affects roughly half the world’s population, doesn’t cause cancer in most people. But in some, the bacterium triggers a chain of damage over many years: it causes chronic inflammation, generates molecules that damage DNA in stomach cells, and interferes with the body’s normal process for destroying damaged cells. Over time, this creates conditions where cells can grow uncontrollably.
H. pylori does this partly by injecting a protein directly into stomach lining cells. That protein hijacks several of the cell’s internal communication systems, disrupting how cells grow, divide, and die. It also weakens the junctions between cells and pushes them toward behaviors normally seen in cancer, like uncontrolled multiplication and the ability to spread.
Diet and Lifestyle Risks
What you eat plays a meaningful role. A large meta-analysis found that high salt intake raises the risk of stomach cancer by about 25%, while moderate salt intake raises it by 20%. High intake of pickled foods increases risk by 28%, and a high intake of processed meat raises it by 24%. Excessive salt damages the stomach lining directly, contributing to the progression from chronic inflammation to precancerous changes. Low consumption of fruits and vegetables and cigarette smoking also increase risk.
The dramatic decline in stomach cancer rates in the United States over the past century, dropping fourfold since 1930, is thought to be largely related to refrigeration replacing salt-based food preservation and overall improvements in diet.
Genetics
A small percentage of stomach cancers are hereditary. The most well-studied form is hereditary diffuse gastric cancer, linked to mutations in a gene called CDH1. About 20 to 40 percent of people with this hereditary syndrome carry a CDH1 mutation. Men with the mutation face a 70 percent lifetime chance of developing stomach cancer, while women face a 56 percent chance. Women with this mutation also have a 40 to 50 percent chance of developing lobular breast cancer.
How Stomach Cancer Is Diagnosed
The primary diagnostic tool is an upper endoscopy, where a thin, flexible tube with a camera is passed through the mouth and into the stomach. This allows a doctor to directly see the stomach lining and take tissue samples (biopsies) from any suspicious areas. Endoscopy with biopsy is the definitive way to confirm stomach cancer.
If cancer is found, an endoscopic ultrasound often follows. This technique uses sound waves from inside the stomach to determine how deeply the tumor has grown into the stomach wall and whether nearby lymph nodes appear affected. In patients without signs of distant spread, endoscopic ultrasound is the first-line method for determining how far the cancer has progressed locally.
Staging and Survival Rates
Stomach cancer is staged based on three factors: how deeply the tumor has invaded the stomach wall (T), whether it has spread to nearby lymph nodes (N), and whether it has metastasized to distant organs (M). These three measurements combine to assign an overall stage.
Survival rates vary enormously by stage at diagnosis. Data from the National Cancer Institute’s SEER program shows five-year survival rates of:
- Localized (cancer confined to the stomach): 78.1%
- Regional (spread to nearby lymph nodes): 39.0%
- Distant (cancer has metastasized to other organs): 8.1%
The gap between localized and distant survival underscores why early detection matters so much. Unfortunately, stomach cancer is often diagnosed at a later stage because early symptoms are easy to overlook.
Treatment
Treatment depends on how advanced the cancer is at diagnosis. For early-stage cancers that haven’t grown deep into the stomach wall, some tumors can be removed during an endoscopy itself, without open surgery. More advanced but still localized cancers typically require surgical removal of part or all of the stomach, often combined with chemotherapy before or after surgery.
For advanced or metastatic stomach cancer, treatment has expanded significantly in recent years. Immunotherapy drugs that help the immune system recognize and attack cancer cells are now used alongside chemotherapy for many patients. In 2023, the FDA approved the immunotherapy drug pembrolizumab combined with chemotherapy as an initial treatment for advanced stomach cancer, regardless of whether the tumor produces certain proteins. For tumors that overproduce a protein called HER2, pembrolizumab can be combined with both a targeted therapy and chemotherapy, though this approach is limited to tumors that also have high levels of a second marker called PD-L1.
Screening and Prevention
The United States does not have routine stomach cancer screening guidelines for the general population. No randomized trials have shown that screening reduces stomach cancer deaths in low-incidence countries like the U.S. Screening may be justified for higher-risk groups: people with chronic atrophic gastritis, those who’ve had part of their stomach surgically removed, people with certain hereditary cancer syndromes, and immigrants from countries where stomach cancer is more common.
In terms of prevention, the most practical steps are treating H. pylori infection if you have one, reducing your intake of heavily salted and processed foods, eating more fruits and vegetables, and not smoking. These won’t eliminate risk entirely, but they address the factors most strongly linked to the disease.