Aspirin may help to treat colon cancer among people who have a particular gene mutation, a new study suggests. The study focused on 964 people with colon cancer. As participants in 2 long-term health studies, they recorded what medicines they took. Researchers looked at the genes in people's colon cancer tumors. They focused on a gene called PIK3CA. This gene is involved in one pathway that promotes the growth of cancer. Aspirin seems to interfere with this pathway. Researchers found that some people in the study had a mutation in the PIK3CA gene. In the first 5 years after diagnosis, 2 of the 62 regular aspirin users with the mutated gene died. In contrast, 23 of 90 people who had the mutation but did not take aspirin died. Researchers also looked at longer-term survival. In the first 13 years after diagnosis, aspirin users who had the mutation were 82% less likely to die of colon cancer than non-users. They were 46% less likely to die of any cause. Experts said testing for the gene could show who might benefit from aspirin. The New England Journal of Medicine published the study. The Associated Press wrote about it October 25.

By Howard LeWine, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Aspirin as we know it today is only a bit older than 100. The Bayer Company began selling this drug in 1899. But the ingredients have been in medical use for more than 3,500 years.

For pennies a day, aspirin relieves pain, reduces fever and soothes achy joints. It became known as the wonder drug. Aspirin got that label even before it started saving lives by treating and preventing heart attacks and strokes.

More recently, aspirin has been making its mark on cancer treatment and prevention. In 2009, a study found that regular aspirin use reduced overall death rates in people with colorectal cancer by 21%. And it reduced deaths actually caused by colorectal cancer 29%. That study was led by Andrew Chan, M.D., of Harvard Medical School. Later studies on aspirin in people with colorectal cancer confirmed these findings.

Like other types of cancer, colorectal cancers are not all the same genetically. They have different mutated genes and different amounts of proteins. In the 2009 study, Dr. Chan's group found that one group of people with colorectal cancer had a particularly longer survival if they used aspirin. People in this group had an extra amount of an enzyme called PTGS2 (formerly known as COX-2) in their cancer cells.

This enzyme plays a big role in inflammation, which leads to pain. It also influences cell growth and the development of cancer. It appears that high PTSG2 interferes with cancer cell death and thereby allows cancer to grow faster. Aspirin blocks the action of the PTGS2 enzyme. This allows natural cancer cell death to occur. As a result, tumor growth slows.

In this new study, Dr. Chan and his colleagues report finding the genetic marker of colorectal cancers that respond to aspirin. It's a mutation of the gene PIK3CA. The PIK3CA mutation is linked to the excess production of PTSG2. Biologically, this helps to explain why the researchers found such a high response rate to aspirin.

What Changes Can I Make Now?

It's too soon to recommend aspirin daily for everyone if the only purpose is to potentially decrease risk of developing colon cancer.

However, if your risk of colon cancer is higher than average, it's worth considering prevention with aspirin. Higher risk is found among people with:

• A prior diagnosis of colon polyps
• A family history of polyps or colon cancer
• A family history of Lynch syndrome, a genetic condition that leads to higher rates of several types of cancer
• A history of ulcerative colitis or Crohn's disease

The best dose of aspirin for cancer prevention is unknown. Talk with your doctor. Currently, I recommend a low dose, such as a baby aspirin (81 milligrams) per day. The main risk of aspirin therapy is bleeding, which always needs to be considered before you start it.

People at average risk of colorectal cancer can help reduce their risk in these ways:

• Get screened with colonoscopy once every 10 years to look for polyps and to have them removed.
• Stay physically active and dedicate time to exercise each day.
• Don't smoke. Use alcohol in moderation or not at all.
• Maintain a healthy body weight.

Although not proven, some other steps may help reduce your colorectal cancer risk. Here's what else you can do:

• Eat a diet rich in fruits and vegetables.
• Get enough vitamin D through sunlight, diet and/or pills.
• Choose whole grain products that provide more fiber.

What Can I Expect Looking to the Future?

This new discovery about response to aspirin in people with colon cancer may dramatically change treatment for some. For example, people with stage 2 or 3 colon cancer and the PIK3CA gene mutation may be advised to take aspirin to prevent the spread of their cancer after surgery. Perhaps they'll even take aspirin instead of chemotherapy.