What Is Gastric Cancer?

Gastric cancer, also known as stomach cancer, can start anywhere in the stomach. The stomach is located in the upper part of the abdomen (the area between the chest and pelvis). It is shaped like a large pouch and its job is to store food while it is being digested.

Gastric cancer begins when the cells of the stomach (usually in the stomach lining) grow and divide without stopping. These cells create lumps (masses) called tumors. Cancerous tumor cells can spread to other parts of the body if they are not treated and eliminated.

About 21,500 people will be diagnosed with gastric cancer in the United States in 2008, according to the American Cancer Society. 

The Stomach

After you chew and swallow your food, the food goes into the esophagus. The esophagus is a tube that carries food through the neck and chest to the stomach.

The stomach is an organ shaped like a large pouch that holds food and starts to digest it. The stomach is located just underneath the lower part of the rib cage on the left side. The stomach produces gastric juice, a liquid that mixes with food. This mixture is then emptied into the first part of the small intestine (duodenum), where it is digested even more.

The stomach has several sections.

The upper parts of the stomach (cardia, fundus, and body) are sometimes called the proximal stomach. Some cells in the upper part of the stomach make acid and pepsin (a digestive enzyme). These parts of the gastric juice help digest food. The upper part includes:

• Cardia - Closest to the esophagus
• Fundus - Next to the cardia
  

The lower sections of the stomach (closest to the intestine) are sometimes called the distal stomach. The distal stomach includes:

• Antrum - Where the food is mixed with gastric juice
• Pylorus - A valve that controls emptying of the stomach contents into the small intestine.
  

The area between the proximal and distal stomach is the body (corpus) of the stomach.

The stomach wall has five layers:

• Inner layer or lining (mucosa) - Glands in the inner layer make juices that help digest food. Most gastric cancers start in this layer.
• Submucosa - Supporting tissue for the inner layer.
• Muscle layer (muscularis) - Muscles that mix and move food.
• Subserosa - Supporting tissue for the outer layer.
• Outer layer (serosa) - Covers the stomach and holds it in place.
  

Cancers that start in different parts of the stomach can cause different symptoms and have different effects. The location can also affect your treatment choices.

How Gastric Cancer Starts

Gastric cancer usually takes many years to develop. Before the cancer actually starts, precancerous changes often begin in the stomach lining. These early changes do not usually cause symptoms, so gastric cancer is rarely detected in its earliest stages.

Gastric cancer begins when cells in the stomach lining begin to grow uncontrollably and form a tumor. The tumor can grow through the stomach’s outer layer into nearby organs, such as the pancreas, esophagus, or intestine (metastasis).

Stomach cancer cells can also travel through the blood to the liver, lungs, and other organs. In addition, these cells can spread through the lymphatic system (a network of tissues and organs that make, store, and carry white blood cells, which fight infection and disease) to lymph nodes (small organs that destroy bacteria and viruses) all over the body.

When cancer spreads from its original place to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the original tumor. For example, if gastric cancer spreads to the lungs, the cancer cells in the lungs are gastric cancer cells. The disease is metastatic gastric cancer, not lung cancer, and it is treated as gastric cancer.

Types of Gastric Cancer

There are several types of gastric cancer.

• Adenocarcinoma - Adenocarcinoma starts in the cells in the innermost lining of the stomach’s mucosa (supporting tissue for the stomach’s outer layer). About 90 percent to 95 percent of all stomach cancers are adenocarcinomas.
  

The other types of gastric cancer are much less common:

• Lymphoma - These cancers of the immune system sometimes start in the stomach wall. Some of them grow quickly, while others grow more slowly. About 4 percent of all gastric cancers are lymphomas.
• Gastrointestinal stromal tumor (GIST) - Scientists believe that these rare tumors start in certain cells (interstitial cells of Cajal) in the wall of the stomach. Some are noncancerous, or benign, but others are cancerous.
• Carcinoid tumor - These tumors start in the stomach’s hormone-making cells. They do not usually spread to other organs. About 3 percent of gastric cancers are carcinoid tumors.
  

Key Statistics

According to the American Cancer Society, 13,190 men and 8,310 women will be diagnosed with gastric cancer in 2008. This disease is most common in older people; the average age at diagnosis is 71. The risk of developing gastric cancer in a person’s lifetime is 1 in 100.

Stomach cancer is much more common in other countries, especially in economically developing countries where it is a leading cause of cancer-related deaths.

This content has been reviewed and approved by Myo Thant, MD.