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While there are several known risk factors for small intestine adenocarcinoma, not much is known about exactly what causes these cancers. In fact, many experts wonder why it’s so rare. The small intestine is the longest part of the gastrointestinal (GI) tract, yet only a very small percentage of GI adenocarcinomas start here.

Scientists have found some DNA changes inside small intestine adenocarcinoma cells that seem to help them grow and spread. DNA is the chemical in each of our cells that makes up our genes, which control how our cells function. We usually look like our parents because they are the source of our DNA. But DNA affects more than just how we look.

Some genes control when cells grow and divide into new cells:

• Certain genes that help cells grow and divide are called oncogenes.
• Genes that help keep cell division under control, cause cells to die at the right time, or help fix mistakes in DNA are called tumor suppressor genes.

Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes.

For example, one cause of these cancers is thought to be problems with the tumor suppressor genes that normally help repair damaged DNA. When one of these genes isn’t working, DNA mistakes aren’t corrected, so gene mutations are passed on to new cells. If enough changes build up inside the cells, it can lead to cancer.

Many small intestine cancers have specific known gene changes, but often it’s not clear what causes these changes. Sometimes they can be inherited from a parent, or they might be caused by things like alcohol or a diet that’s high in red meats. But sometimes the gene changes that lead to small intestine cancer seem to occur for no apparent reason. Many of the changes are probably just random events that sometimes happen inside a cell, without having an outside cause.

Gene changes inside cells can build up over a person’s lifetime, which might help explain why small intestine cancer largely affects older people.