Helicobacter pylori eradication as a preventive tool against gastric cancer.

Helicobacter pylori (H. pylori), which increases the risk of gastric diseases, including digestive ulcers and gastric cancer, is highly prevalent in Asian countries. There is no doubt that eradication of the bacterium is effective as a treatment of digestive ulcer, but eradication aiming to reduce the gastric cancer risk is still controversial. Observational studies in Japan demonstrated that the eradication decreased the gastric cancer risk among 132 stomach cancer patients undergoing endoscopical resection (65 treated with omeprazol and antibiotics and 67 untreated). In Columbia, 976 participants were randomized into eight groups in a three-treatment factorial design including H. pylori eradication, resulting in significant regression in the H. pylori eradication group. A recent randomized study in China also showed a significant reduction of gastric cancer risk among those without any gastric atrophy, intestinal metaplasia, and dysplasia. Efficacy of eradication may vary in extent among countries with different incidence rates of gastric cancer. Since the lifetime cumulative risk (0 to 84 years old) of gastric cancer in Japan is reported to be 12.7% for males and 4.8% for females (Inoue and Tominaga, 2003), the corresponding values for H. pylori infected Japanese can be estimated at 21.2% in males and 8.0% in females under the assumptions that the relative risk for infected relative to uninfected is 5 and the proportion of those infected is 0.5. Both the fact that not all individuals are infected among those exposed and the knowledge that only a small percentage of individuals infected with the bacterium develop gastric cancer, indicate the importance of gene-environment interactions. Studies on such interactions should provide useful information for anti-H. pylori preventive strategies.

Precise definition of anonymization in genetic polymorphism studies.

Anonymization is an essential tool to protect privacy of participants in epidemiological studies. This paper classifies types of anonymization in genetic polymorphism studies, providing precise definitions. They are: 1) unlinkable anonymization at enrollment without a participant list; 2) unlinkable anonymization before genotyping with a participant list; 3) linkable anonymization; 4) unlinkable anonymization for outsiders; and 5) linkable anonymization for outsiders. The classification in view of accessibility to a table including genotype data with directly identifiable data such as names is important; if such tables exist, staff may obtain genotype information about participants. The first three modes are defined here as anonymization unaccessible to genotype data with directly identifiable information for research staff. Anonymization with a key code held by participants is possible with any of the above anonymization modes, by which participants can access to their own genotypes through telephone or internet. A guideline issued on March 29, 2001 with collaboration of three Ministries in Japan defines "anonymization in a linkable fashion" and "anonymization in an unlinkable fashion", "for the purpose of preventing the personal information from being divulged externally in violation of law, the present guidelines or a research protocol", but the contents are not clear in practice. The proposed definitions will be useful when we describe and discuss the preferable mode of anonymization for a given polymorphism study.