18. Epidemiology and Biostatistics Division
The Epidemiology and Biostatistics Division has planned and conducted independent and collaborative studies on cancer etiology and prevention, with special focus on dietary factors. Several epidemiological projects are currently in progress including case-control, cohort and intervention studies. In addition, collaborative studies in the field of clinical and basic sciences are conducted through providing statistical design, analysis and data processing support.
Etiological Role of Diet and Nutrients in Cancer
Diet has been implicated as playing an etiological role in cancer occurrence and is considered to contribute to the unique patterns of cancer incidence in Japan. However, to date, epidemiologic evidence regarding this issue has been limited. Our division has therefore initiated a population-based prospective study on diet and cancer in collaboration with the Cancer Information and Epidemiology Division and the National Cardiovascular Center in which about 100,000 individuals have been followed for 10 years. The dietary questionnaire commonly used in epidemiologic studies in Japan has a serious limitation in terms of estimating the dietary intakes of individuals. Perceptions of change in diet did not improve the estimation of past intake among individuals in retrospective studies.(198) Seasonal variability in dietary intake was associated with a marked diminution of reproducibility over time.(199,200) Our division has therefore developed a semiquantitative food frequency questionnaire, based on an analysis of dietary data collected from the regions in which the prospective study was conducted. This questionnaire includes items concerning the average consumption frequencies of 138 foods as well as 14 supplementary questions on qualitative aspects of the diet. Utilizing this specialized survey format, we were able to obtain not only the average long-term intake of individual food items but also semiquan-titative estimates of the consumption of 15 major nutrients. The questionnaire was applied to 50,000 subjects participanting in this prospective study in five Public Health Center districts in February of 1995.
An investigation to assess the reproducibility and validity of the present questionnaire, which is currently underway, involves verification by means of four 7-day food records and the collection of two blood and urine samples from 250 subjects.
Environmental and Genetic Interaction in the Etiology of Human Cancer
Patterns of cancer incidence vary by ethnicity and change with migration which results in intermingling with other populations. These facts suggest an interaction between environmental and genetic factors in cancer occurrence. Our division has been conducting several epidemiological studies in Brazil, a multi-ethnic nation with 1.2 million people of Japanese ancestry, in collaboration with A. C. Camargo Hospital and São Paulo University.(201) A case-control study of lung cancer in Brazil, suggested that the risk of cigarette smoking was synergistically related to the exon 7 polymorphism of CYP1A1.(202,203) A case-control study of gastric cancer is also ongoing in Brazil. A questionnaire and blood components have been collected from 101 Japanese and 250 non-Japanese patients with gastric cancer and their controls in the São Paulo area.The environmental and genetic factors will be analyzed and compared in cases and controls in two sets of different ethnic groups.
A Randomized Controlled Field Trial to Prevent Gastric Cancer with Vitamin C and Beta-carotene in a High-risk Population
Observational epidemiologic studies suggest that the risk of gastric cancer is increased in individuals with chronic atrophic gastritis and decreased in those with high consumption of vitamin C and beta-carotene. After the feasibility of a large-scale population-based intervention study was confirmed by a small pilot study, a randomized controlled trial to assess the effectiveness of vitamin C and beta-carotene supplements on gastric cancer incidence was initiated for individuals with chronic atrophic gastritis in a district where the mortality rate is one of the highest in Japan. In the first year of subject recruitment, 439 out of 602 eligible subjects (73%) have agreed to participate in the trial and started to take one of four possible regimens by a two-by-two factorial design with two levels of vitamin C (50 or 500 mg/day) and beta-carotene (0 or 15 mg/day).
Statistical Support for Clinical and Basic Cancer Research
Data management systems as a statistical center have been developing for multi-institutional collaborative studies and have been used for 61 clinical trials including 22 phase III trials operated by the Japan Clinical Oncology Group. A total of 974 patients have been registered into the database from these clinical trials in 1995, which summed up to 10,000 patients. Statistical support regarding protocol development and data analysis has been provided for clinical and basic research projects.(15,204)
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