I was surprised to read that gastric (stomach) cancer is the second leading cause of cancer deaths worldwide. It's less common in the United States. The American Cancer Society estimated 21,000 new diagnoses of stomach cancer for Americans in 2010. For women, estimated deaths from gastric cancer and cervical cancer are very similar: for 2010, the numbers are 4,220 for gastric cancer and 4,210 from cervical cancer. Most of us get Pap smears every year to catch pre-cancerous polyps and prevent cervical cancer. Why aren't we trying to protect ourselves from gastric cancer?
Gastric and cervical cancers have something else in common. Both are strongly associated with infectious agents. Human papillomavirus is recognized as the cause of most cervical cancers, and a vaccine has already been developed. Helicobacter pylori is recognized as the cause of most gastric cancer. Unlike viral infections, H. pylori infection can be cured fairly easily with antibiotics since the pathogen is a bacteria. Early treatment of H. pylori infections could potentially prevent these cancers.
In the United States, five-year survival rates from gastric cancer are less than 15 percent, according to Reference 2. This paper also reports that H. pylori is the most common bacterial infection worldwide, but only a small fraction of infected people go on to develop gastric cancer. H. pylori may not be required for the development of cancer, but its attributable risk is reported as 75 percent.
A review from the Veterans Affairs Medical Center and Baylor College of Medicine identifies six major strains of H. pylori. These differ greatly in their ability to cause cancer. In east Asia, both infection rates and gastric cancer rates are high. In parts of south Asia and Africa, infection rates are high but gastric cancer rates are low. The authors suggest that screening tests for H. pylori should include data on the particular strain.
The development of gastric cancer is thought to include many steps. Inflammation is believed to produce changes in the stomach lining that favors tumor growth, as well as lower acidity which increases the formation of carcinogenic nitroso compounds from nitrates and nitrites in the diet. The authors of Reference 3 suggest H. pylori eradication for patients at highest risk.
References:
1. Statistics from the American Cancer Society:
http://www.cancer.org/acs/groups/content/@epidemiologysurveilance/documents/document/acspc-026238.pdf
2. Polk DB et al, “Helicobacter pylori: gastric cancer and beyond”, Nat Rev Cancer. 2010 June; 10(6): 402-14.
3. Yanaoka Y et al, “Geographic differences in gastric cancer incidence can be explained by differences between Helicobacter pylori strains”, Internal Medicine 2008; 47: 1077-83.
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.