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Understanding the causes of gastric and esophageal cancers

The latest study linking a diet high in animal products with an increased risk of certain cancers is one in a series of reports we have published since conducting the large-scale study. These reports have added to the small but growing body of information about potential causes of these cancers, which are among the fastest increasing cancers in the western world.

These cancers are very aggressive and hard to treat, so it's important to determine factors contributing to the rise. While no single study is ever enough to prompt widespread changes in lifestyle or medical practice, our study is consistent with earlier findings that diet and lifestyle do play a role.

Research methods
When it comes to cancer research, Connecticut is a model for the rest of the country. We have the oldest tumor registry in the country, which allows us to assess incidence changes over decades. The NCI selected us, in part, also because we have a rapid reporting system in place through the Yale Cancer Center. Our cancer center staff traveled to hospitals across the state gathering and analyzing information on a weekly basis. We asked those patients with cancer if they wished to participate and thereby contribute to our understanding of these cancers.

The role of diet
The public should be aware of the limits to what we found. For this latest study, we focused on dietary nutrients versus the specific types of foods eaten every day. For example, we looked at fiber intake, which was strongly associated with a reduced incidence of all four types of cancers studied. But this in itself raises additional questions. Was it the fiber itself that made the difference? Or was it because people who eat lots of fruits and vegetables and whole grains take in more fiber and something in those foods had the protective effect? We can't be sure.

Nitrites, which are found in smoked and salted animal products, are another example. Was it the nitrites themselves that were a cause of cancer or were they merely markers that told us a person ate a lot of animal products? We don't know the exact answer. But we can say that a person who eats a diet low in plant foods and high in animal products has a three- to four-fold greater chance of getting these cancers, compared to someone who eats a diet high in plant foods and low in animal products.

A somewhat surprising result was that a high starch diet was a risk factor. But again, this may be indicative of a dietary pattern of people eating high starch foods in place of vegetables and fruits.

Obesity a strong risk factor
It should be pointed out that in an earlier analysis we published from these same data, obesity was most strongly linked to these types of cancers. When we examined time trends in risk factors, the one thing that has changed dramatically over the past two decades is the increased prevalence of obesity.

Esophageal and gastric cancer risk factors
Gastric cancers develop over a long period of time, which in theory allows for intervention to stop the cancers from developing.

Past studies have shown that having reflux disease puts people at higher risk for esophageal adenocarcinoma. Over time, the reflux condition causes changes in the cells that line the esophagus. This condition, called Barrett's esophagus, is a known risk factor for EAC but is easily diagnosed.

By researching the factors, such as diet, that potentially fuel these changes, we could help slow or stop the progression of healthy tissue into cancerous tissue. For example, we now know that drinking alcohol and smoking are linked to an increase in these and other types of esophageal cancers. In addition, controlling obesity may be one way to reduce the incidence of these cancers. So we can offer patients at higher risk for such cancers the chance to decrease the incidence of these cancers by changing their lifestyles.

Broad benefits
Indeed, these findings are consistent with general guidelines put forth in recent years to prevent cancers and other diseases. The American Cancer Society, for example, recommends reducing the amount of red meat in your diet. We know that by controlling obesity, stopping or reducing smoking and limiting alcohol intake, you reduce the risk of certain cancers, as well as heart disease and other chronic conditions, such as diabetes. So it's certainly the prudent thing to do.

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Dr. Susan Mayne leads the Cancer Prevention and Control Research Program for the Yale Cancer Center. She is also an epidemiologist and an associate professor of epidemiology at the Yale University School of Public Health.