Stomach Cancer Facts

This is the first page in the What is Stomach Cancer Guide. This guide was developed by the HealthTree Education Team.

Cancer begins when cells in the body start to grow out of control. Stomach cancer, also called gastric cancer, starts in the cells that line the inside of the stomach. The stomach is a hollow, muscular organ in the upper left part of the abdomen that stores and breaks down food before it passes to the small intestine. When you have stomach cancer, cells in the stomach do not follow the normal cell cycle. Healthy cells grow, copy themselves, and then die. Cancer cells change, grow faster than normal, and do not die the way they should.

It is important to understand the difference between cancer that starts in the stomach and cancer that spreads to the stomach from another organ. Cancer that starts in the stomach is called primary stomach cancer. This guide is about primary stomach cancer.

What does the stomach do?

The stomach is a muscular, bag-like organ that plays an important role in digestion. Its main jobs include:

• Storing food after you eat and mixing it with digestive juices

• Breaking down food into a liquid form using acid, enzymes, and muscular contractions

• Moving partially digested food into the small intestine, where most nutrients are absorbed

• Producing a protein called intrinsic factor, which is needed for the body to absorb vitamin B12

Because the stomach plays such an important role in digestion and nutrition, stomach cancer and its treatment can affect eating, weight, and the absorption of nutrients. Understanding these effects can help you and your care team plan for nutritional support throughout your care.

How stomach cancer starts

Most stomach cancers develop over many years through a gradual process. Long-term infection with H. pylori causes inflammation in the stomach lining. Over time, this inflammation can cause the normal stomach lining cells to be replaced with a different type of cell, a process called intestinal metaplasia. Some of these changed cells can develop further abnormalities, become dysplastic, and eventually turn into cancer. This process typically takes ten to twenty years or more.

Not everyone who is infected with H. pylori develops stomach cancer. Other factors, including diet, smoking, and genetic susceptibility, also influence whether a person develops cancer. Researchers continue to study how these factors interact to cause stomach cancer.

How does stomach cancer affect the body?

How stomach cancer affects the stomach

Stomach cancer can grow through the layers of the stomach wall. As it grows, it can interfere with the stomach's ability to store and digest food, causing symptoms such as pain, nausea, early fullness when eating, and weight loss. Tumors can also bleed, leading to anemia and fatigue.

How stomach cancer affects nearby organs

The stomach lies close to the esophagus, small intestine, pancreas, spleen, liver, and large bowel. As stomach cancer grows, it can spread to these nearby organs. It can also spread to the lining of the abdominal cavity, a condition called peritoneal carcinomatosis, which can cause fluid buildup in the abdomen.

How stomach cancer affects the lymph nodes and other organs

Stomach cancer can spread to lymph nodes in the abdomen. It can also spread to distant organs through the bloodstream. When stomach cancer spreads beyond the stomach and nearby structures, it most commonly travels to the liver, lungs, peritoneum, and bones. Spread to other parts of the body is called metastasis.

Types of stomach cancer

Several types of cancer can start in the stomach. The most important ones are:

• Adenocarcinoma. This is by far the most common type of stomach cancer, making up about 90 to 95 percent of cases. It starts in the glandular cells that line the inside of the stomach. When doctors refer to stomach cancer, they almost always mean adenocarcinoma. Adenocarcinomas of the stomach are further divided into two main subtypes based on their appearance under the microscope: the intestinal type, which tends to be better differentiated and more closely linked to H. pylori, and the diffuse type, which is less differentiated, tends to spread more widely through the stomach wall, and is more likely to be hereditary in some cases.

• Gastrointestinal stromal tumor. Often called a GIST, this type of cancer starts in the cells that control the movement of the stomach muscles. GISTs are not adenocarcinomas and are treated quite differently. They are often driven by specific gene mutations, such as mutations in the KIT or PDGFRA genes.

• Gastric lymphoma. Cancer of the lymph tissue in the stomach wall. The most common type is mucosa-associated lymphoid tissue lymphoma, often called MALT lymphoma, which is closely linked to H. pylori infection.

• Neuroendocrine tumors. Tumors that start in hormone-producing cells of the stomach. Most gastric neuroendocrine tumors are slow-growing, but some can be aggressive.

• Carcinosarcoma and other rare types. A small number of stomach cancers are rare types with features of multiple cell types.

Related conditions

Certain conditions are closely linked to stomach cancer risk and are important to understand:

• Helicobacter pylori infection. H. pylori is a bacterium that lives in the stomach lining and is one of the most important causes of stomach cancer worldwide. It is also the main cause of most peptic ulcers. H. pylori is treatable with antibiotics. Testing for and treating H. pylori reduces the risk of stomach cancer.

• Chronic atrophic gastritis. Long-term inflammation of the stomach that causes the stomach lining to thin and lose its normal glands. It is often caused by H. pylori and is a precancerous condition.

• Intestinal metaplasia. A condition in which the normal stomach lining is replaced with tissue that looks like the lining of the intestine. It is considered a precancerous change and is often found in people with H. pylori infection.

• Gastric polyps. Growths on the inside of the stomach lining. Most are benign, but some types, particularly adenomatous polyps, carry an increased risk of becoming cancerous.

• Hereditary diffuse gastric cancer syndrome. A rare inherited condition caused by mutations in the CDH1 gene. People with this syndrome have a very high lifetime risk of developing diffuse-type stomach cancer.