There are many known risk factors for stomach cancer, but itis not known exactly how these factors cause cells of the stomach lining to become cancerous. This is the subject of ongoing research.

Several changes that are thought to be pre-cancerous can occur in the stomach lining.

One of these is atrophic gastritis. This is a condition where the normal glands of the stomach are either decreased or absent. There is some degree of inflammation (the stomach cells are damaged by cells of the immune system), which is often due to H. pylori infection. It is not known exactly why this condition progresses to cancer.

Another change that may also be pre-cancerous is intestinal metaplasia. This is a condition where the normal lining of the stomach is replaced with cells that closely resemble the cells that usually line the intestine. People with this condition usually have chronic atrophic gastritis as well. How and why this change occurs and progresses to stomach cancer is not well understood. This might also be related to H. pylori infection.

Recent research has provided clues to how some stomach cancers form. For instance, H. pylori bacteria, particularly certain subtypes, can convert some of the chemicals in some foods into chemicals that cause mutations (changes) in the DNA of the cells in the stomach lining. This may also explain why certain foods such as preserved meats increase a person's risk for stomach cancer. On the other hand, some of the foods that lower stomach cancer risk contain antioxidants, which can block substances that damage a cell's DNA.

During the past few years, scientists have made a lot of progress in understanding how certain changes in DNA can cause normal stomach cells to grow abnormally and form cancers. DNA is the chemical in each cell that carries our genes - the instructions for how our cells function. We look like our parents because they are the source of our DNA. But DNA affects more than how we look.

Some genes contain instructions for controlling when cells grow and divide. Certain genes that promote cell division are called oncogenes. Others that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes.

There are also genes that make enzymes to repair the DNA when it develops abnormal changes. If these genes are lost or damaged, it can also lead to some cancers.

Inherited abnormalities of some of these types of genes (as explained in the section "What are the risk factors for stomach cancer?") can increase a person's stomach cancer risk. But most of the genetic changes that lead to stomach cancer occur after birth. Inherited genetic changes account for only a small percentage of stomach cancers.

Last Medical Review: 11/03/2009
Last Revised: 11/03/2009