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Treating an infection to prevent a cancer: H. pylori and stomach cancer

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The number of newly diagnosed stomach cancer cases in the United States is less than a tenth of the number of prostate cancer cases or breast cancer cases, which may be part of the reason it doesn’t get the same attention as breast and prostate cancer. But the mortality rate is much higher for stomach (or gastric) cancer. Nearly 11,000 Americans will likely die from gastric cancer this year, with only 28 percent of cases surviving five years or more. For comparison, the five-year survival rate for prostate cancer is nearly 99 percent and for breast cancer, it’s more than 89 percent.

On a global scale, an estimated 700,000 people will die from gastric cancer this year, as Stanford infectious disease specialist Julie Parsonnet, MD, and her co-authors note in a Viewpoint piece in the most recent issue of the Journal of the American Medical Association. The authors also point out that worldwide, about 77 percent of gastric cancer cases are linked to chronic infections of Helicobacter pylori, a helix-shaped bacteria that was identified in the early 1980s and found to be linked to gastric ulcers a few years later, as well as to gastritis, an inflammation of the stomach lining that is a precursor to stomach cancer.

Researchers are still trying to understand exactly how H. pylori causes cancer or even how it colonizes the gastrointestinal track - they believe it's picked up via food or water. Until recently, there was a dearth of randomized clinical trials that looked at the effectiveness of screening and treatment for H. pylori as a method for preventing stomach cancer.

Ignoring gastric cancer in the hope that it will soon disappear is not a tenable health policy

In the opinion piece, the authors describe the recommendations of a working group that met in December 2013 at the behest of the International Agency for Research on Cancer. Taking the burden of the disease and the availability of treatment options in consideration, the group considered gastric cancer “a logical target for intervention,” according to the authors of the JAMA piece. They go on to write:

Screening and treatment for H pylori is generally acceptable and affordable. An inexpensive serological test can determine who may be infected, with a sensitivity and specificity that could be sufficient for population-based prevention programs. Low-cost treatment regimens using 2 or 3 generic antibiotics plus a proton pump inhibitor for 7 to 14 days can eradicate the infection in more than 80% of cases, depending on the antibiotic resistance patterns of H pylori within the population. Economic modeling studies indicate that H pylori screening and treatment strategies are cost-effective under a large range of assumptions about effectiveness and costs. However, the models are limited by reliance on observational data rather than randomized trial results, by a lack of information on possible adverse effects of treatment, and by limited data from lower-income countries.

Researchers still have many gaps in their understanding of the best methods to prevent stomach cancer, but several trials may answer some of those questions in the coming decade.

Stomach cancer is not the only cancer known to be linked with an infection. Doctors routinely test whether women who come in for a PAP smear are infected with the human papilloma virus (HPV), which is linked to cervical cancer. Chronic hepatitis B and C infections are known to be linked to liver cancer. In time, screening for H. pylori to prevent stomach cancer may become routine. Until then, Parsonnet and her coauthors say in their conclusion, "Ignoring gastric cancer in the hope that it will soon disappear is not a tenable health policy."

Previously: Researchers identify potential drug target in ulcer bug that infects half the world’s population, Good-bye cancer, good-bye stomach: A survivor shares her tale and Image of the Week: Helicobacter pylori colonizing the stomach
Photo by Shuman Tan and Lydia-Marie Joubert

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