Esophageal cancer has a high fatality rate, and is the sixth most common cause of cancer death worldwide. Over the last century, a wide variety of environmental factors have been suspected: hot drinks, carbonated drinks, pickled vegetables, human papillomavirus, and many others. A team of researchers at the National Cancer Institute recently performed an extensive literature search for evidence on each of these proposed risk factors.
There are two primary types of esophageal cancer, with somewhat different risk factors. Until the 1970's, over 90 percent of these cancers worldwide were esophageal squamous cell carcinoma. Today esophageal adenocarcinoma is the dominant type in the United States. The two types are approximately equal in many Western countries, but the squamous cell variety is still more common in other parts of the world. Thus, traditional observations may have more relevance to squamous cell than to adenocarcinoma.
Here are the top ten risk factors according to demonstrated associations:
1. Gastroesophageal acid reflux disease (GERD). This is the most important risk for adenocarcinoma, which accounts for the majority of cases in the United States.
2. Tobacco use. Smoking increases the risk of adenocarcinoma by a factor of two, and squamous cell carcinoma by a factor of three to seven.
3. Alcohol. Excessive consumption (three or more drinks per day) increases the risk of squamous cell carcinoma by a factor of three to five. The association with adenocarcinoma is less clear.
4. Yerba mate, a drink made from the herb Ilex paraguayensis, which is popular in some areas of South America.
5. Gastric atrophy, which reduces the stomach's production of acid. This may allow bacteria to grow and produce carcinogens.
6. Achalasia, a motility disorder of the esophagus.
7. Poor diet, with low amounts of fruits and vegetables.
8. Low socioeconomic status, poor oral hygiene, and tooth loss. The mechanisms are not clear.
9. Industrial chemicals, including polyaromatic hydrocarbons and acetaldehyde.
10. Obesity.
On the positive side, aspirin and other non-steroidal anti-inflammatory drugs are associated with a lower risk of esophageal cancer. A reduction in inflammation may provide protection. In addition, infection with Helicobacter pylori, while increasing the risk of gastric cancer, appears to lower the risk of esophageal cancer. The authors suggest that the decline in H. pylori infection rates through improved hygiene could be partly responsible for the rise of esophageal adenocarcinoma.
The authors recommended further study on the effects of medications that relax the lower esophageal sphincter. These include asthma drugs, calcium channel blockers, nitroglycerine, and benzodiazepines.
Reference:
Kamangar F et al, “Environmental causes of esophageal cancer”, Gastroenterol Clin North Am. 2009 March; 38(1): 27-vii.
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.