Stomach Cancer Prevention

Who Is at Risk?

People at elevated risk for gastric cancer include older adults with atrophic gastritis or pernicious anemia; patients with sporadic gastric adenomas,[1] familial adenomatous polyposis,[2] or hereditary nonpolyposis colon cancer;[3] and immigrant ethnic populations from countries with high rates of gastric carcinoma.[4,5] Workers in the rubber and coal industries are also at increased risk.[6]

Risk factors for gastric cancer include the presence of precursor conditions such as chronic atrophic gastritis and intestinal metaplasia, pernicious anemia, and gastric adenomatous polyps. Genetic factors include a family history of gastric cancer, Li Fraumeni syndrome, and type A blood type.[6] Environmental factors include low consumption of fruits and vegetables; consumption of salted, smoked, or poorly preserved foods; cigarette smoking; and radiation exposure.[6-8]

There is consistent evidence that Helicobacter pylori infection, also known as H. pylori infection, of the stomach is strongly associated with both the initiation and promotion of carcinoma of the gastric body and antrum and of gastric lymphoma.[9-11] The International Agency for Research on Cancer classifies H. pylori infection as a cause of noncardia gastric carcinoma and gastric, low-grade, B-cell mucosa-associated lymphoid tissue or mucosa-associated lymphatic tissue (MALT) lymphoma (i.e., a Group 1 human carcinogen).[12,13] Gastric cancer has been observed to be more common among individuals who use proton pump inhibitors (PPIs), relative to nonusers, after apparent successful H. pylori eradication therapy.[14] However, confounding and detection bias cannot be ruled out as explanations.

There is consistent and solid evidence that Epstein-Barr virus (EBV) infection is strongly associated with gastric cancer. A systematic review and meta-analysis of 71 articles (4 from the United States) assessed the prevalence and association of EBV and gastric cancer. EBV infection was associated with a large increase in gastric cancer risk. The pooled prevalence of EBV in 20,361 patients with gastric cancer was 8.77% (95% confidence interval [CI], 7.73%–9.92%; I2 statistic, 83.2%). Results were consistent across studies, although heterogenous. The pooled odds ratios (ORs) for gastric cancer were 18.56 (95% CI, 15.68–21.97; I2 statistic, 55.4%) for studies (kappa statistic, 20; n = 4,116 patients with cancer) with matched pairs design (including tumor and tumor-adjacent normal tissues) and 3.31 (95% CI, 0.95–11.54; I2 statistic, 55.0%) for studies with nonmatched pairs design. The proportion of EBV-associated gastric cancer among males was significantly higher than among females (10.8% vs. 5.7%) (P < .0001). However, the pooled OR estimate for EBV-associated gastric cancer was significantly higher among females (21.47; 95% CI, 15.55–29.63; I2 statistic, 0%) than among males (14.07; 95% CI, 10.46–18.93; I2 statistic, 49.0%) (P = .06). EBV was more prevalent in the cardia (12.5%) and the body (11.7%) compared with the antrum (6.3%) (P = .0002).[15]

Compared with the general population, people with duodenal ulcer disease may have a lower risk of gastric cancer.[16]

Interventions for Reduction of Stomach (Gastric) Cancer Risk

Interventions With Inadequate Evidence as to Whether They Reduce the Risk of Stomach (Gastric) Cancer

Smoking Cessation

Studies have shown that smoking is a key risk factor for gastric cancer. A systematic review and meta-analysis showed a 60% increase in gastric cancer in male smokers and a 20% increase in gastric cancer in female smokers compared with nonsmokers.[1] Another systematic review of studies addressed the relationship between cigarette smoking and gastric cancer by estimating the magnitude of the association for different levels of exposure to cancer. It provides solid evidence that smoking is the most important behavioral risk factor for gastric cancer.[1-3] The risk of stomach cancer decreases among former smokers, compared with persistent smokers, with time since cessation. The pattern that emerges from these observations makes it reasonable to infer that cigarette smoking prevention or cessation would result in a decreased risk of gastric cancer.

H. Pylori Infection Eradication

Helicobacter pylori infection is an accepted cause of gastric adenocarcinoma.[4,5] Questions remain concerning the natural history of H. pylori infection, and the mechanism of transmission and the rates of reinfection or recrudescence for different populations are unknown.[6,7] A small randomized trial of antibiotic eradication in 140 H. pylori-infected people suggested the possibility of transmission among close family members.[8] In 70 participants, only the participant received eradication therapy; in the other 70 participants, all H. pylori-infected family members living with the primary participant also received the eradication therapy. Nine months after the therapy, the positivity rates in the index participants in each group were 38.6% and 7.1%, respectively (odds ratio, 8.61; 95% confidence interval [CI], 2.91–22.84), suggesting the possibility of transmission from untreated, infected family members.

Because about half of the world population is infected with H. pylori, antibacterial treatment for all people who are chronically infected may be impractical and could trigger antimicrobial resistance. Vaccination against H. pylori has been shown effective in experimental animal models. Such efficacy has not been studied in humans.

A randomized controlled trial (RCT) of 3,365 participants from a nutritionally deprived population showed that short-term treatment with amoxicillin and omeprazole reduced the incidence of gastric cancer by 39% during a period of 15 years following randomization.[9] With follow-up to 22 years, H. pylori treatment was associated with an absolute reduction in the risk of gastric cancer death of 16 cases per 1,000 individuals. For vitamin supplementation, the absolute risk reduction was 19 cases per 1,000 individuals; for garlic supplementation, it was 10 cases per 1,000 individuals. H. pylori treatment and vitamin supplementation were also associated with absolute reductions in gastric cancer incidence of 33 cases and 19 cases per 1,000 individuals, respectively.[10]

The magnitude of benefit of treating H. pylori in populations with different levels of gastric cancer risk has been unclear. A systematic review and meta-analysis of RCTs and observational studies assessed the treatment of H. pylori with curative regimens for three different clinical scenarios:[11]

The authors found 24 eligible studies (22 from Asia) with 715 incident gastric cancers among 48,000 individuals in 340,000 person-years of follow-up. Individuals with eradication treatment for H. pylori had a lower incidence of gastric cancer (pooled incidence rate ratio, 0.53; 95% CI, 0.44–0.64). Treatment was associated with a substantially lower risk in individuals who had asymptomatic infection (pooled incidence rate ratio, 0.62; 95% CI, 0.49–0.79) and in individuals after endoscopic resection of gastric cancer (pooled incidence rate ratio, 0.46; 95% CI, 0.35–0.60). Risk was not lower in those in the lowest tertile of gastric cancer incidence. Limitations of the study included a lack of consideration of the negative effects of treatment, such as antibiotic resistance of H. pylori and other microorganisms. In addition, eradication of H. pylori might reduce a postulated protective effect of H. pylori for esophageal adenocarcinoma. The results may have implications for the treatment of some subgroups of individuals at particularly high risk for stomach cancer, such as Asian immigrant populations in the United States and individuals with underlying gastric mucosal disease such as atrophic gastritis. The results may also have implications for the prevention of recurrent gastric cancer.[11]

Proton pump inhibitor (PPI) use is associated with worsening of gastric atrophy, particularly in H. pylori–infected individuals. One study analyzed 63,397 patients who were included in a territory-wide health database in Hong Kong. These patients had been treated for H. pylori between 2003 and 2012 and had appeared to be cleared of the infection. The results suggested more than a twofold increase in risk of gastric cancer for those who used PPIs after H. pylori treatment, relative to those who did not use PPIs after H. pylori treatment.[12] Because the finding could be caused by residual confounding or detection bias, its relevance to clinical practice is uncertain.

Diet

Excessive salt intake has been identified as a possible risk factor for gastric cancer in correlation and case-control studies.[1] The daily intake of salt has decreased drastically in most Western countries and in Japan, in part due to public health campaigns to reduce hypertensive diseases. This may be at least partially responsible for declines in gastric cancer rates. There is a consistent association between high salt intake and the risk of gastric cancer.

Epidemiological evidence from case-control and cohort studies suggests that increased intake of fresh fruits and vegetables is associated with decreased gastric cancer rates.[2,3] However, no randomized controlled trials have been done to establish a causal association.

Dietary Supplements

Because of the evidence for an inverse association between gastric cancer and dietary intake of fruits and vegetables, especially those rich in antioxidants, there has been interest in dietary supplementation with antioxidants.

Dietary indices of micronutrient intake have been calculated and indicate possible protective effects of beta carotene, vitamin A, vitamin E, selenium, vitamin C, or foods that contain these compounds. A chemoprevention trial in China reported a statistically significant reduction in the gastric cancer mortality rate after supplementation with beta carotene, vitamin E, and selenium.[4] The population studied, however, may have been nutritionally deficient, raising questions of generalizability to other populations such as that of the United States. In addition, the experimental design did not permit assessment of the relative effects of beta carotene, vitamin E, and selenium.

Likewise, there was a randomized placebo-controlled trial of 200 mg of oral allitridum (a component of garlic) every day combined with 100 mcg of oral selenium every other day for 1 month of each year over a 3-year period. The study took place in Qixia County (Shandong Province, China), an area with low intake of garlic and low selenium content in their garlic compared with other areas of China.[5] Although designed as a double-blinded trial, researchers noted that allitridum causes a distinctive garlic odor. Investigators randomly assigned 5,033 people, who met at least one of the following criteria: (1) medical history of stomach disorder, (2) family history of tumor, (3) history of smoking, or (4) history of alcohol consumption. The study, published in a Chinese medical journal, was not well described. After a follow-up of up to 11 years, there were 23 gastric cancer cases in the allitridum/selenium group and 30 cases in the placebo group (relative risk [RR] after adjustment for several baseline characteristics, 0.48; 95% confidence interval [CI], 0.21–1.06). Only 60% of the gastric cancers were diagnosed by histopathology. There was a qualitative difference in outcome by sex: RR_men, 0.36 (95% CI, 0.14–0.92); RR_women, 1.14 (95% CI, 0.22–5.76). Given the problems with design and reporting of the study, the evidence of benefit (including men) was weak and may not be generalizable to Western countries.

In a randomized, double-blind, chemoprevention trial in Venezuela among a population at increased risk for gastric cancer, a combination of antioxidant vitamins (vitamins C, E, and beta carotene) failed to modify progression or regression of precancerous gastric lesions.[6] Another potential explanation for the lack of benefit of vitamin supplementation in this trial was the high prevalence of advanced premalignant lesions and the high Helicobacter pylori infection rate.[7]

A secondary analysis of the Alpha-Tocopherol Beta Carotene trial conducted in male smokers in Finland evaluated the effect of supplementation on gastric cancer incidence.[8] No protective effects for these supplements against gastric cancer were observed. Six-year follow-up results of a study of 976 Colombian patients have been reported. Patients were randomly assigned to receive eight different treatments that included vitamin supplements and anti-H. pylori therapy either alone or in combination versus placebo. Among the 79 patients who received anti-H. pylori therapy, a borderline statistically significant regression of intestinal metaplasia compared with a placebo (15% vs. 6%; RR, 3.1; 95% CI, 1.0–9.3) was noted. However, the combinations of antibiotics and vitamins did not confer additional benefits. More importantly, the progression rate of intestinal metaplasia was comparable regardless of the treatments received. The progression rate was 23% in the placebo group and 17% in antibiotic recipients.[9]

A systematic review examined randomized trials of antioxidant dietary supplements for the prevention of gastrointestinal cancers, including gastric cancer.[10] Twenty trials were identified that assessed the preventive effects of antioxidant supplements or vitamin C on gastrointestinal cancer. With regard to gastric cancer, there were 12 comparisons of one or more micronutrients with placebo: beta-carotene alone (4 trials); vitamin C alone (1 trial); vitamin E alone (1 trial); vitamin A plus beta-carotene (1 trial); beta-carotene plus vitamin C (1 trial); beta-carotene plus vitamin E (1 trial); beta-carotene plus vitamins C and E (1 trial); selenium plus vitamins C and E (1 trial); and beta-carotene, vitamins C and E, and selenium (1 trial). None of the comparisons showed a statistically significant effect on the incidence of gastric cancer. The overall summary estimate across all trials of antioxidants showed no statistically significant effect (RR of gastric cancer, 1.14; 95% CI, 0.97–1.33). After treatment of 2.1 to 12 years and follow-up for as many as 14.1 years, approximately 0.51% of participants in the combined antioxidant groups developed gastric cancer versus 0.38% in the placebo groups. In the combined analysis of all 20 trials of antioxidants for the prevention of gastrointestinal cancers, a fixed effects model showed an increase in overall mortality for antioxidants compared with placebo (RR for mortality, 1.04; 95% CI, 1.02–1.07). A random effects model showed no such increase (RR for mortality, 1.02; 95% CI, 0.97–1.07).