Japanese Journal of Clinical Oncology Advance Access originally published online on June 29, 2005
Japanese Journal of Clinical Oncology 2005 35(7):404-411; doi:10.1093/jjco/hyi114
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© 2005 Foundation for Promotion of Cancer Research
Evaluation Based on Systematic Review of Epidemiological Evidence Among Japanese Populations: Tobacco Smoking and Total Cancer Risk
1 Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, 2 Division of Epidemiology, Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai, 3 Division of Epidemiology and Prevention, Aichi Cancer Center Research Institute, Nagoya, 4 Department of Epidemiology & Preventive Medicine, Gifu University School of Medicine, Gifu, 5 Department of Preventive Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka and 6 Department of Preventive Medicine, Faculty of Medicine, Saga University, Saga, Japan
For reprints and all correspondence: Manami Inoue, Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan. E-mail: mnminoue{at}gan2.res.ncc.go.jp
Received February 15, 2005; accepted May 15, 2005
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Abstract |
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 TOP Abstract INTRODUCTIONMETHODSMAIN FEATURES AND COMMENTSEVALUATION OF EVIDENCE ON...References |
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Background: We evaluated the association between tobacco smoking and total cancer risk among Japanese populations based on a systematic review of epidemiological evidence.
Methods: Original data were obtained from searches of MEDLINE using PubMed, complemented with manual searches. Evaluation of associations was based on the strength of evidence and the magnitude of association, together with biological plausibility as previously evaluated by the International Agency for Research on Cancer. Meta-analysis of associations was also conducted to obtain summary estimates of association.
Results: A total of eight cohort studies were identified. In men, all studies consistently showed a moderately increased risk of total cancer in current smokers compared with never-smokers. In women, an increase in risk was seen but was weaker than in men. The summary relative risk was estimated as 1.53 (95% confidence interval 1.41–1.65).
Conclusion: We conclude that there is convincing evidence that current tobacco smoking moderately increases the risk (
1.5 times) of total cancer in the Japanese population compared with never-smoking Japanese.
Key Words: systematic review • epidemiology • tobacco smoking • total cancer • Japanese
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INTRODUCTION |
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TOPAbstractINTRODUCTIONMETHODSMAIN FEATURES AND COMMENTSEVALUATION OF EVIDENCE ON...References |
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In Japan, lifestyle-related diseases such as cancer have been recognized as major components of the overall pattern of disease for decades, and the importance of the prevention of cancer by lifestyle modification is now strongly acknowledged. Various international and domestic guidelines and recommendations based on the epidemiological evidence for cancer prevention have appeared, with notable examples from the International Agency for Research on Cancer (IARC) (1), World Cancer Research Fund and American Institute for Cancer Research (2), World Health Organization and Food and Agriculture Organization (WHO/FAO) (3) and Harvard Center for Cancer Prevention (4). Evidence for these has for the most part been derived from Western populations, ensuring their suitability for these populations. Given that the host and environmental factors of Japanese populations are not always the same as those of the West, however, these guidelines may be incompletely relevant to Japanese. It is therefore important to evaluate the existing epidemiological evidence derived from Japanese populations, and from these derive relevant recommendations regarding major risk factors of cancer applicable to Japanese.
Our research group has investigated the association between health-related lifestyles and total cancers, as well as the five major cancer sites in Japan, namely the stomach, colon and rectum, liver, lung and breast. Findings were summarized and the magnitude of the effect of each lifestyle on cancer was assessed based on previous publications targeting Japanese populations. The present study focuses on the association between tobacco smoking and total cancer risk among Japanese populations.
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METHODS |
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TOPAbstractINTRODUCTIONMETHODSMAIN FEATURES AND COMMENTSEVALUATION OF EVIDENCE ON...References |
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Original data for this review were identified by searches of MEDLINE using PubMed, complemented by manual searches of references from relevant articles where necessary. All epidemiological studies on the association between tobacco smoking and total cancer incidence or mortality among Japanese from 1966 to 2004, including papers in press if available, were identified using the search terms ‘tobacco smoking’, ‘cancer’, ‘risk’, ‘cohort study’, ‘case–control study’ and ‘Japan’ as keywords found in the abstract. Papers written in either English or Japanese were reviewed, and only studies on Japanese populations living in Japan were included. Individual results were summarized in the tables separately by study design as cohort or case–control studies.
Evaluation was made based on the strength of evidence and the magnitude of association. First, relative risks in each epidemiological study were grouped by magnitude of association, with consideration of statistical significance (SS) or no statistical significance (NS), as strong, <0.5 or >2.0 (SS); moderate, either (i) <0.5 or >2.0 (NS), (ii) >1.5–2 (SS) or (iii) 0.5 to <0.67 (SS); weak, either (i) >1.5–2 (NS), (ii) 0.5 to <0.67 (NS) or (iii) 0.67–1.5 (SS); or no association, 0.67–1.5 (NS). Criteria for the magnitude of association are summarized in Table 1. After this process, overall magnitude of association was judged using the same criteria as for magnitude of association, together with the strength of evidence in a similar manner to that used in the WHO/FAO Expert Consultation Report (3), in which evidence was classified as ‘convincing’, ‘probable’, ‘possible’ and ‘insufficient’ (Table 2). We assumed that biological plausibility corresponded to the judgment of the most recent evaluation from the IARC (1). Notwithstanding the use of this quantitative assessment rule, arbitrary assessment cannot be avoided when there is considerable variation in the magnitude of association between the results of each study. The final judgment, therefore, is made based on the consensus of research group members, and is not necessarily objective.
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In addition, when there was ‘convincing’ or ‘probable’ evidence of a positive or inverse association, meta-analysis was conducted to obtain summary estimates of the association. In general, studies which reported relative risks and their confidence intervals (CIs) by comparing current smokers with never-smokers were included in the meta-analysis, but for those which categorized risk values separately according to smoking amount, such as the number of cigarettes smoked or pack-year index, meta-analysis was conducted to estimate summary risk values for current smokers, and these values were then used for further meta-analysis. In the case of multiple publication of analyses of the same or overlapping data sets, only data from the largest or most updated results were included, and incidence was given priority over mortality as an outcome measure. Incidence was also given priority in single publications describing both incidence and mortality. Studies without information on CIs and different reference categories were excluded from meta-analysis. General variance-based methods were used to estimate summary statistics and their 95% CIs. Heterogeneity among studies was examined by testing the Q statistic, with the model used to determine summary relative risk and its 95% CI, namely a random or fixed effect model, selected according to the statistical significance in the Q statistic. Meta-analysis was done using the meta command of STATA statistical package version 8 (13).
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MAIN FEATURES AND COMMENTS |
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TOPAbstractINTRODUCTIONMETHODSMAIN FEATURES AND COMMENTSEVALUATION OF EVIDENCE ON...References |
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A total of eight cohort studies were identified (Table 3). Among them, four presented results by gender (7,9,11,12), one for men only (5), and one for men and women combined only (8). No case–control studies of the association between tobacco smoking and total cancer risk were identified.
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After excluding two studies due to the unavailability of a point estimate or CIs (6,9) and one due to a shorter study analysis period than another study of the same population (10), four results for men, three for women and one for men and women combined were available for further evaluation. A summary of the magnitude of association for these studies is shown in Table 4. In men, all studies consistently showed a moderately increased risk (
) of total cancer in current smokers compared with never-smokers. The study with men and women combined also showed moderately increased risk. The increase in risk in women was weaker than that in men, with two studies showing a weakly increased risk () and one showing no association (–).
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The summary relative risk was estimated by meta-analysis using a random effect model (test for heterogeneity: Q = 23.364 with df = 7, P = 0.001) as 1.53 (95% CI 1.41–1.65) for men and women combined, 1.64 (95% CI 1.55–1.73) for men and 1.34 (95% CI 1.24–1.43) for women (Fig. 1).
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In the IARC evaluation (1), no evaluation was made on tobacco smoking and total cancer risk. However, the study concluded that tobacco smoking and tobacco smoke are carcinogenic to humans, and that there was sufficient evidence of a causal relationship in humans with most sites of cancer. We therefore assumed that the association between tobacco smoking and total cancer risk holds biological plausibility.
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EVALUATION OF EVIDENCE ON TOBACCO SMOKING AND TOTAL CANCER RISK IN JAPANESE |
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TOPAbstractINTRODUCTIONMETHODSMAIN FEATURES AND COMMENTSEVALUATION OF EVIDENCE ON...References |
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From these results and assumed biological plausibility, we conclude that there is convincing evidence that current tobacco smoking moderately increases the risk of total cancer in the Japanese population compared with never-smoking Japanese (
1.5 times, or 1.6 in men and 1.3 in women). |
Acknowledgments |
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The authors gratefully acknowledge the assistance of Ms Izumi Suenaga in this report. This work was supported by the Third Term Comprehensive 10-year Strategy for Cancer Control from the Ministry of Health, Labour and Welfare, Japan.
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References |
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TOPAbstractINTRODUCTIONMETHODSMAIN FEATURES AND COMMENTSEVALUATION OF EVIDENCE ON...References |
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1 International Agency for Research on Cancer. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Volume 83. Tobacco Smoke and Involuntary Smoking. Lyon, France: IARC 2004.
2 World Cancer Research Fund/American Institute for Cancer Research. Food, Nutrition and the Prevention of Cancer: A Global Perspective. Washington, DC: American Institute for Cancer Research 1997.
3 World Health Organization. WHO Technical Reports Series 916. Diet, Nutrition, the Prevention of Chronic Disease. Report of a joint WHO/FAO Expert Consultation. Geneva: WHO 2003.
4 Colditz GA, Atwood KA, Emmons K, Monson RR, Willett WC, Trichopoulos D, et al. Harvard report on cancer prevention volume 4: Harvard cancer risk index. Cancer Causes Control 2000;11:477–88.[CrossRef][ISI][Medline]
5 Kono S, Ikeda M, Tokudome S, Nishizumi M, Kuratsune M. Smoking and mortalities from cancer, coronary heart disease and stroke in male Japanese physicians. J Cancer Res Clin Oncol 1985;110:161–4.[CrossRef][ISI][Medline]
6 Kono S, Ikeda M, Tokudome S, Nishizumi M, Kuratsune M. Cigarette smoking, alcohol and cancer mortality: a cohort study of male Japanese physicians. Jpn J Cancer Res 1987;78:1323–8.[ISI][Medline]
7 Hirayama T. Life-style and mortality. A large-scale census-based cohort study in Japan. Contributions to Epidemiology and Biostatistics Volume 6. Basel, Switzerland: Karger 1990.
8 Akiba S. Analysis of cancer risk related to longitudinal information on smoking habits. Environ Health Perspect 1994;102(Suppl 8):15–9.
9 Takezaki T, Tajima K, Yoshida M, Tominaga S. Risk of death by health habit index from a cohort study among the residents of a rural area in Aichi, Japan. Nippon Koshu Eisei Zasshi 1999;46:904–4 (in Japanese).[Medline]
10 Hara M, Sobue T, Sasaki S, Tsugane S. Smoking and risk of premature death among middle-aged Japanese: ten-year follow-up of the Japan Public Health Center-based prospective study on cancer and cardiovascular diseases (JPHC Study) cohort I. Jpn J Cancer Res 2002;93:6–14.[ISI][Medline]
11 Kawaminami K, Minowa M, Okayama A, Hayakawa T, Ueshima H. An association (population attributable fraction) between smoking habit and mortality from all causes, cancer and lung cancer: NIPPON DATA80, 1980–1999. National Integrated Projects for Prospective Observation of Non-communicable Diseases and its Trend in the Aged. Nippon Eiseigaku Zasshi 2003;57:669–73 (in Japanese).[Medline]
12 Inoue M, Hanaoka T, Sasazuki S, Sobue T, Tsugane S, JPHC Study Group. Impact of tobacco smoking on subsequent cancer risk among middle-aged Japanese men and women: data from a large-scale population-based cohort study in Japan—the JPHC study. Prev Med 2004;38:516–22.[Medline]
13 Stata Corporation. Stata Statistical Software, Special Edition, 8.2 for Windows. Texas: Stata Corporation 2004.
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