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The common ulcer-causing bug linked this summer to reduced rates of childhood asthma and allergies may also help protect adults against one type of cancer, according to a new analysis. Researchers report today in the journal Cancer Prevention Research that they found the stomach microbe Helicobacter pylori(H. pylori) may help prevent a major form of cancer of the esophagus (the muscular tube that carries food and drink from the throat to the stomach).
Esophageal cancer will strike an estimated 16,470 new patients and result in 14,280 deaths in the U.S. this year alone, according to the National Cancer Institute (NCI) in Bethesda, Md.
There are two varieties of the disease: squamous cell carcinoma, which affects the flat cells lining the upper part of the esophagus, and adenocarcinoma, which typically involves mucus-producing cells present in the lower region. Both types are most common in adults (particularly males) over 60 and generally are not diagnosed until late stages when patients begin exhibiting symptoms such as difficulty swallowing, a chronic cough, hoarseness, and pain in the throat or between the shoulder blades.
Until the mid-1970s, esophageal adenocarcinoma was relatively rare worldwide. Since then, its incidence has quadrupled in the U.S., and around 1990 it surpassed the squamous cell variety as the major form of esophageal cancer. Despite the alarming rise of this deadly disease in developed nations, cases of adenocarcinoma remain scarce in developing countries. Physicians speculate that obesity and acid reflux may be risk factors for this form of esophageal cancer, whereas smoking and heavy alcohol use play a significant role in squamous cell carcinoma.
Surgical removal of esophageal tumors is the most common treatment for both types of the disease. Radiation and chemotherapy can be used to relieve pain and enhance swallowing, especially in patients who are not good candidates for surgery. Because esophageal cancers can spread to the liver, lungs, bones and brain, the prognosis for patients diagnosed at late stages is poor. According to the American Cancer Society, less than 20 percent of all esophageal cancer patients in the U.S. survive for more than five years past their initial diagnosis.
Over the past century, global rates of the bacterium H. pylori have also changed dramatically. Since the dawn of humanity, this microbe has thrived in the stomach, usually colonizing children by age 10. But with improved sanitation and the rise of antibiotics, H. pylori rates have declined sharply in the U.S. and western Europe with only 5 percent of kids now testing positive by age 10. Although some children may acquire the bug later in life, rates of H. pylori among adults remain much lower in the U.S. in comparison to the developing world.
With the rapid rise of esophageal adenocarcinoma paralleling the disappearance of the microbe in developed countries, a slew of studies have emerged over the past decade examining the potential role of H. pylori in preventing this cancer. Using data from 19 prior publications, Farin Kamangar, an NCI epidemiologist, created a virtual study comparing over 1,700 cases of esophageal cancer with 5,600 controls.
Using statistical tests, Kamangar combined the results from studies in the U.S., Europe, Iran, China and Japan to evaluate if H. pylori helps prevent either form of esophageal cancer in such a large and geographically diverse sample pool.
Although the presence of H. pylori showed no association to rates of squamous cell carcinoma, the bug appears to safeguard against esophageal adenocarcinoma, Kamangar says. Just how the microbe prevents this cancer remains unknown, but he speculates that H. pylori infection may reduce acid production in the stomach, thereby diminishing reflux into the esophagus—a major risk factor for adenocarcinoma (which occurs in the area of the esophagus closest to the stomach).
Despite the microbe's possible beneficial effects, however, Steven Moss, a gastroenterologist at Brown University, notes that "most people would be hesitant to propose keeping H. pylori infections" as they can lead to ulcers and gastric cancer. Ultimately, Moss says, the work adds another piece to the "continuing story that this infection, which was always thought to be bad, may also have positive health effects."