Maryland Oncology Hematology

Gastric Cancer Screening & Prevention

Overview

Information about the prevention of cancer and the science of screening appropriate individuals at high-risk of developing cancer is gaining interest. Physicians and individuals alike recognize that the best “treatment” of cancer is preventing its occurrence in the first place or detecting it early when it may be most treatable.

Gastric cancer is characterized by the presence of cancer cells in the tissues of the stomach, which is located in the upper abdomen. Gastric cancer is currently the second leading cause of cancer death worldwide.

The chance of an individual developing cancer depends on both genetic and non-genetic factors. A genetic factor is an inherited, unchangeable trait, while a non-genetic factor is a variable in a person’s environment, which can often be changed. Non-genetic factors may include diet, exercise, or exposure to other substances present in our surroundings. These non-genetic factors are often referred to as environmental factors. Some non-genetic factors play a role in facilitating the process of healthy cells turning cancerous (i.e. the correlation between smoking and lung cancer) while other cancers have no known environmental correlation but are known to have a genetic predisposition. A genetic predisposition means that a person may be at higher risk for a certain cancer if a family member has that type of cancer.

Heredity or Genetic Factors

Researchers are beginning to identify genetic factors that contribute to the development of gastric cancer in some individuals. Specifically, the E-cadherin gene (CDH1) has been associated with a high risk of gastric cancer. Hereditary diffuse gastric cancer is a rare and deadly form of gastric cancer that can result from CDH1 mutations. Parents who carry this genetic mutation have a 50% chance of passing it along to their offspring. Three out of four people who inherit this genetic mutation will eventually develop gastric cancer.

Environmental or Non-Genetic Factors

Several risk factors have been associated with an increased risk of developing gastric cancer. These include infection with the Helicobacter pylori (H. pylori) bacteria, smoking, low fat and protein consumption, high nitrate consumption, low dietary vitamin A and C and consumption of smoked foods. Exposure to a carcinogen called ptaquiloside has also been linked to gastric cancer. In addition, poor drinking water and a lack of refrigeration appear to contribute to the development of gastric cancer.

H. Pylori: The primary risk factor associated with gastric cancer is infection with the bacteria, Helicobacter Pylori (H. pylori). In fact, 85% to 95% of all gastric cancers are believed to be caused by this infection.

Helicobacter Pylori (H. pylori) infection is common and spreads through food or water contaminated with fecal matter. Infection with H. pylori causes a reduction in the normal acid production and a shrinkage and loss of cells (called atrophy) in the stomach. Atrophy of the stomach, in particular, is considered to be a precancerous condition. It can take decades for the precancerous conditions caused by H. pylori infection to develop into cancer. Individuals who live in regions that have high gastric cancer rates are often plagued with H. pylori stomach infections that develop early in life.

Ptaquiloside: Researchers performed an epidemiological study in Merida, Venezuela, where there is an unusually high incidence of gastric cancer, and found a correlation between the incidence of gastric cancer and the presence of a fern called Pteridium spp. The fern contains a toxic compound called ptaquiloside that is toxic to humans. In this study, the researchers found ptaquiloside in milk from the local cattle. The cattle grazed in pastures where the fern was prevalent. The researchers observed that the risk of developing gastric cancer was 3.6 times higher in the highlands, where the fern is prevalent, than in the adjacent control state.

Prevention

Cancer is largely a preventable illness. Two-thirds of cancer deaths in the U.S. can be linked to tobacco use, poor diet, obesity and lack of exercise. All of these factors can be modified. Nevertheless, an awareness of the opportunity to prevent cancer through changes in lifestyle is still under-appreciated.

Some studies have indicated that eradication of the H. pylori infection may prevent gastric cancer. Specifically, antibiotics, antioxidants and aspirin have been shown to reduce the risk of gastric cancer because they prevent the progression of gastric precancerous conditions.

Antibiotics and Antioxidants: Researchers conducted a study in the province of Nariño, Columbia, in the Andes Mountains, a region with some of the highest stomach cancer rates in the world. The study involved 631 individuals from this province who had stomach lining biopsies that showed precancerous changes. The subjects were assigned to receive one of eight treatments: 1) anti-H. pylori antibiotics, 2) beta carotene, 3) beta carotene with antibiotics, 4) vitamin C, 5) vitamin C with antibiotics, 6) beta carotene with vitamin C, 7) beta carotene with vitamin C and antibiotics, and 8) placebo. The subjects were followed for six years, at which time they had another stomach lining biopsy.

After 6 years, the researchers studied whether the precancerous conditions in the subjects progressed, regressed or did not change. Individuals who received anti-H. pylori antibiotics, beta carotene, vitamin C or a combination of any of these treatments were three to five times more likely than those of the placebo group to have regression of their precancerous condition. The researchers found that both the single and combined treatments were equally as effective. The researchers concluded that their results support the theory that eliminating H. pylori infections through treatment with antibiotics or antioxidants is a promising approach that may prevent the development of stomach cancer in high-risk populations.

Aspirin: Aspirin is a type of non-steroid anti-inflammatory drug (NSAID). Researchers have long speculated that NSAIDs might reduce the risk for gastric and other types of cancer. In order to investigate this theory, researchers in Sweden conducted a population-based case-control study in 5 Swedish countries. The researchers interviewed 567 individuals with gastric cancer and 1165 control subjects. Among the interview questions were questions regarding the use of pain relievers. The researchers found that aspirin users had a moderately reduced risk of gastric cancer when compared with never users. The risk of gastric cancer was reduced as the frequency of aspirin use increased. While the results indicated a relationship between aspirin and gastric cancer risk, they did not establish a clear association between gastric cancer risk and non-aspirin NSAIDs or other pain relievers. The researchers concluded that aspirin may play a role in reducing the risk of gastric cancer.

Diet: Diet is a fertile area for immediate individual and societal intervention to decrease the risk of developing certain cancers. Numerous studies have provided a wealth of often-contradictory information about the detrimental and protective factors of different foods.

There is convincing evidence that excess body fat substantially increases the risk for many types of cancer. While much of the cancer-related nutrition information cautions against a high-fat diet, the real culprit may be an excess of calories. Studies indicate that there is little, if any, relationship between body fat and fat composition of the diet. These studies show that excessive caloric intake from both fats and carbohydrates lead to the same result of excess body fat. The ideal way to avoid excess body fat is to limit caloric intake and/or balance caloric intake with ample exercise.

It is still important, however, to limit fat intake, as evidence still supports a relationship between cancer and polyunsaturated, saturated and animal fats. Specifically, studies show that high consumption of red meat and dairy products can increase the risk of certain cancers. One strategy for positive dietary change is to replace red meat with chicken, fish, nuts and legumes.

High fruit and vegetable consumption has been associated with a reduced risk for developing at least 10 different cancers. This may be a result of potentially protective factors such as carotenoids, folic acid, vitamin C, flavonoids, phytoestrogens and isothiocyanates. These are often referred to as antioxidants.

There is strong evidence that moderate to high alcohol consumption also increases the risk of certain cancers. One reason for this relationship may be that alcohol interferes with the availability of folic acid. Alcohol in combination with tobacco creates an even greater risk of certain types of cancer.

Exercise: Higher levels of physical activity may reduce the incidence of some cancers. According to researchers at Harvard, if the entire population increased their level of physical activity by 30 minutes of brisk walking per day (or the equivalent energy expenditure in other activities), we would observe a 15% reduction in the incidence of colon cancer.

Screening and Early Detection

For many types of cancer, progress in the areas of cancer screening and treatment has offered promise for earlier detection and higher cure rates. The term screening refers to the regular use of certain examinations or tests in persons who do not have any symptoms of a cancer but are at high risk for that cancer. When individuals are at high risk for a type of cancer, this means that they have certain characteristics or exposures, called risk factors that make them more likely to develop that type of cancer than those who do not have these risk factors. The risk factors are different for different types of cancer. An awareness of these risk factors is important because 1) some risk factors can be changed (such as smoking or dietary intake), thus decreasing the risk for developing the associated cancer; and 2) persons who are at high risk for developing a cancer can often undergo regular screening measures that are recommended for that cancer type. Researchers continue to study which characteristics or exposures are associated with an increased risk for various cancers, allowing for the use of more effective prevention, early detection and treatment strategies.

Gastric cancer rates have been steadily declining in the United States and at this point, routine screening for this cancer is not performed. However, gastric cancer is still the leading cause of cancer in Japan, accounting for 18% of cancer deaths there. Mass screening programs for gastric cancer have been most effective in high-risk areas, such as Japan. Early gastric cancer has a high cure rate when it is surgically removed. In some Japanese studies, as many as 40% of newly diagnosed patients have early gastric cancer and as many as 60% of patients are actively participating in mass screening programs. Routine screening in Japan involves gastroscopy.

Gastroscopy: A gastroscopy is an examination performed through an endoscope, which is a flexible tube inserted through the esophagus that allows the physician to visualize, photograph and biopsy (sample) the cancer. All patients have a gastroscopy with a biopsy to determine the histology or appearance of the cancer under the microscope.