Stomach Cancer Awareness Month: H. Pylori Infection & Cancer Risk

November is Stomach Cancer Awareness Month. This is a good time to learn about stomach cancer and its causes, risk factors, symptoms, treatment, and prevention. Stomach cancer, also known as gastric cancer, develops when cells in the stomach begin to grow uncontrollably. Stomach cancer tends to develop slowly over many years without symptoms, leaving cancer undetected.

The stomach is made up of five main parts. The first three parts make up the proximal stomach. The cardia is closest to the esophagus. The fundus is the upper part of the stomach next to the cardia. The body, or corpus, is the main and largest part of the stomach, in between the upper and lower stomach. The last two parts of the stomach make up the distal stomach. The antrum is the lower part of the stomach near the small intestine where food mixes with gastric juices. The last part of the stomach, the pylorus, is the lowest part of the stomach and acts as a valve to control the emptying of the stomach into the small intestine.

The stomach wall is also made up of five layers. The innermost layer is the mucosa, where stomach acid and digestive enzymes are made. Most stomach cancers begin in the mucosa. The second layer is the submucosa, which is a supporting layer. The third layer is the muscularis propria, a thick layer of muscle that moves and mixes stomach contents. The two final outermost layers are the subserosa and serosa, which wrap around the stomach. 

The different parts and layers of the stomach are important to understand because they determine the type of stomach cancer and how it develops. Cancers of the top portion of the stomach near the esophagus are called cardia stomach cancer, and cancers of the other areas of the stomach are non-cardia cancers. The type and location of stomach cancer greatly affects the prognosis and treatment options as well. If cancer develops past the mucosa layer, stomach cancer becomes more advanced and treatment may be more extensive.

About 26,000 new stomach cancer cases will be diagnosed in the United States in 2021. About 11,000 will die from stomach cancer. This makes up about 1.5 percent of all cancers diagnosed in the United States each year. Stomach cancer is more prevalent in other areas of the world, such as Asia and South America and is a leading cause of death worldwide.

Stomach cancer used to be one the leading cancers in the United States in the early 20th century. However, stomach cancer incidence has dropped significantly in recent years. Researchers believe this is largely due to increased food refrigeration, which decreases the amount of smoked and heavily salted foods we consume, and a decline in the number of people infected with Helicobacter pylori (H. pylori) bacteria. H. pylori is a major cause of stomach cancer, especially non-cardia cancers in the distal (lower) part of the stomach.

H. pylori is a bacteria that can enter the body and live in the stomach and digestive tract. People get H. pylori through contaminated food and water or contact with saliva or other bodily fluids of infected people. It is most common in areas of the world without sanitation and access to clean water, and about 60 percent of people in the world are infected with H. pylori.

The bacteria typically lives in the body for many years, attacking the stomach lining over time. This may damage the stomach lining enough for acid to get through, and in some people this can cause ulcers, or sores, to develop, as well as bleeding and other gastric symptoms. For others, H. pylori doesn’t cause any symptoms and may go unnoticed for years. If detected, H. pylori infection can typically be treated with antibiotics.

Prior to the discovery of H. pylori, researchers believed that ulcers were caused by spicy foods or stress. In 1982, Dr. Robin Warren, a pathologist in Australia, observed a small, curved bacteria growing in the lower stomach of patients with stomach biopsies, as well as inflammation in the stomach lining. With a colleague, Dr. Barry Marshall, Dr. Warren conducted a study examining stomach biopsies of 100 patients. The study found that the recently discovered bacteria was present in almost all patients with gastric inflammation and ulcers. Based on these results, Drs. Warren and Marshall proposed this bacteria, later named H. pylori, was responsible for ulcers and other gastric symptoms. 

Their discovery was supported by future studies and animal models. But still, scientists were skeptical. Without an option to test their theories on people, Dr. Marshall decided to test the only person he could ethically recruit: himself! He drank H. pylori cultured bacteria in a broth, knowing he could later treat himself with antibiotics. He soon developed gastritis symptoms, such as stomach pain, bad breath, and vomiting, all precursors to ulcers. After 10 days, Dr. Marshall received an endoscopy and found the same H. pylori bacteria in his gut, proving the gastric symptoms were the result of H. pylori once and for all.

After the H. pylori discovery, researchers began to speculate that the bacteria may also be linked to stomach cancer. A 2001 analysis of 12 H. pylori and stomach cancer studies from the 1990s determined that people with H. pylori infection were six times more likely to develop stomach cancer than those who were uninfected. In addition, a cancer prevention study conducted in the 1980s and 1990s in Finland studied 243 people with stomach cancer compared to a control group, testing each participant for H. pylori antibodies. The study found that those with non-cardia stomach cancers were 8 times more likely to be infected with H. pylori than the control group. 

Overall, researchers have determined that on average people with H. pylori infection are about six times more likely to develop stomach cancer than those who are not infected. Recent studies have shown that nearly 90 percent of stomach cancer cases are associated with H. pylori infection.

Research is ongoing to determine exactly how H. pylori increases stomach cancer risk. Scientists suspect that the ongoing inflammatory response that H. pylori causes may predispose cells to becoming cancerous but further research is needed. Researchers are also working to determine why H. pylori may lead to cancer in some individuals and not others, and if there may be a genetic component affecting risk, as well as if certain strains of H. pylori are more likely to cause cancer. Finally, researchers continue to work to find the best treatments for H. pylori and stomach cancer, as well as a vaccine for H. pylori infection, especially as antibiotic resistance has increased.