Tobacco smoking and gastric cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

BACKGROUND: We evaluated the association between tobacco smoking and gastric cancer risk among the Japanese population based on a systematic review of epidemiologic evidence. METHODS: Original data were collected by 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 evaluated previously by the International Agency for Research on Cancer. RESULTS: Ten cohort studies and 16 case-control studies were identified. In men, most studies reported moderate or strong positive associations between smoking and gastric cancer. In women, the positive association was weaker than in men. Of eight studies (three cohort studies and five case-case control studies), two cohort and three case control studies reported a weakly to strongly increased risk of gastric cancer. The summary relative risk for current smokers was estimated to be 1.56 (95% confidence intervals 1.36-1.80), 1.79 (1.51-2.12), 1.22 (1.07-1.38) for the total population, men and women, respectively. CONCLUSION: We conclude that there is convincing evidence that tobacco smoking moderately increases the risk of gastric cancer among the Japanese population.     

Evaluation based on systematic review of epidemiological evidence among Japanese populations: tobacco smoking and total cancer risk

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 ( approximately 1.5 times) of total cancer in the Japanese population compared with never-smoking Japanese.     

Alcohol drinking and breast cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

BACKGROUND: We reviewed epidemiological studies on alcohol drinking and breast cancer among the Japanese population. This report is one among a series of articles by our research group evaluating the existing evidence concerning the association between health-related lifestyles and cancer. METHODS: Original data were obtained from MEDLINE searches using PubMed or from searches of the Ichushi database, 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. RESULTS: Three cohort studies and eight case-control studies were identified. There were inconsistent results regarding alcohol drinking and breast cancer risk among cohort studies. A significant positive association was observed in one, but another showed nonsignificant inverse association. Out of the eight case-control studies, two studies showed a significantly increased risk among women who drink daily and who had higher intake of alcohol, respectively. Experimental studies have supported the biological plausibility of a positive association between alcohol drinking and breast cancer risk. CONCLUSION: We conclude that epidemiologic evidence on the association between alcohol drinking and breast cancer risk remains insufficient in terms of both the number and methodological quality of studies among the Japanese population.     

Tobacco smoking and lung cancer risk: an evaluation based on a systematic review of epidemiological evidence among the Japanese population

BACKGROUND: Although tobacco smoking is the best established risk factor for lung cancer, the association is not as strong among Japanese as among Western populations. It would be of value, therefore, to quantify that association in Japan based on a systematic review of epidemiological evidence for the primary prevention of lung cancer. METHODS: Original data were obtained from MEDLINE searches using PubMed, supplemented with manual searches. The evaluation of associations was based on the strength of evidence and the magnitude of the association, together with biological plausibility as previously evaluated by the International Agency for Research on Cancer. A meta-analysis was also conducted to estimate the summary measure of those associations. RESULTS: A total of 8 cohort studies and 14 case-control studies were identified, almost all of which consistently showed a strong association of current smoking with the risk of lung cancer. The summary relative risk for current smokers versus never smokers was estimated as 4.39 (95% confidence interval 3.92-4.92) for men and 2.79 (95% confidence interval 2.44-3.20) for women. Cohort studies and case-control studies gave reasonably consistent summary measures. The summary relative risks were 11.7 and 2.30 for squamous cell carcinoma and adenocarcinoma, respectively, in men, and were 11.3 and 1.37 correspondingly in women. CONCLUSION: There is convincing evidence that tobacco smoking strongly increases the risk of lung cancer in the Japanese population, with the relative risk for current smokers compared with never smokers measuring around 4.4 for men and 2.8 for women.     

Tobacco smoking and colorectal cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

BACKGROUND: It is unclear whether tobacco smoking is related to colorectal cancer risk in Japan. We evaluated the association among the Japanese population based on a systematic review of epidemiologic evidence. METHODS: Original data were obtained from searches of MEDLINE using PubMed, complemented with manual searches. The 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. RESULTS: A total of six cohort studies and 15 case-control studies were thus identified. A substantial degree of heterogeneity was observed in the association between smoking and colon cancer; most case-control studies published before 1994 reported an inverse association, whereas studies conducted over the last decade did not find any significant association. Recent cohort studies have shown a non-significant 20-40% increase in colon cancer risk associated with current smoking. Several recent case-control studies and some cohort studies have identified a weak to strong positive association between smoking and rectal cancer. CONCLUSION: We conclude that tobacco smoking possibly increases the risk of colorectal cancer among the Japanese population. More specifically, tobacco smoking may possibly increase the risk of rectal cancer; however, epidemiologic evidence is still insufficient to demonstrate any clear association with colon cancer.     

Association between Smokeless Tobacco Use and Waterpipe Smoking and the Risk of Lung Cancer: A Systematic Review and Meta-Analysis of Current Epidemiological Evidence

Background: Smokeless tobacco and waterpipes are used by hundreds of millions of people worldwide and consumption rates exceed that of cigarette smoking in much of South East Asia and parts of the Middle East. However, the cancer risks of these methods of tobacco consumption are less well-characterized than those of cigarette smoking. The objective of this study was to systematically review the epidemiological evidence on the association between smokeless tobacco use and waterpipe smoking and lung cancer risk. Methods: The MEDLINE, EMBASE, Web of Science and OpenSIGLE databases were searched to identify eligible case-control and cohort studies (published before 1st December 2020 in any language) that adjusted for cigarette smoking or included non-cigarette smokers only. Summary odds ratio/relative risk estimates and confidence intervals were extracted, and pooled risk ratios (RRs) for lung cancer were calculated using random effects meta-analysis. Results: The literature search identified 2,465 publications: of these, 26 studies including 6,903 lung cancer patients were included in the synthesis (20 studies of smokeless tobacco use, five of waterpipe smoking, one of both). Our results suggest that smokeless tobacco use is associated with an increased risk of lung cancer among non-cigarette smokers, and that betel quid tobacco may be particularly hazardous. The random effects meta-analysis showed that exclusive use of any type of smokeless tobacco (pooled RR = 1.53, 95%CI 1.09 – 2.14), betel quid chewing (pooled RR = 1.77, 95%CI 1.06 – 2.95), and waterpipe smoking (pooled RR = 3.25, 95%CI 2.01 – 5.25) were significantly associated with an increased risk of lung cancer. Conclusions: This meta-analysis of case-control/cohort studies supports the hypothesis that use of smokeless tobacco and waterpipe smoking is associated with increased risk of developing lung cancer. Considering the widespread and increasing use of smokeless tobacco in developing countries, and increasing prevalence of waterpipe smoking in almost all societies, these findings inform formulation of public health policy, legislation and tobacco control measures at national and international level to increase awareness and decrease the prevalence of smokeless tobacco use and waterpipe smoking.     

Alcohol drinking and lung cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

BACKGROUND: The relationship between alcohol consumption and risk of lung cancer is controversial. Based on a systematic review of epidemiologic evidence, we evaluated this association among the Japanese population, who may be more susceptible to alcohol-related diseases than Western populations. METHODS: Original data were obtained from MEDLINE searches using PubMed or from searches of the Ichushi database, complemented with manual searches. The 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. RESULTS: We identified seven cohort studies and two case-control studies. One cohort study demonstrated a strong positive association between alcohol drinking and the risk of female lung cancer, but the association almost disappeared after adjustment for smoking. The other eight studies showed a weak positive or no association. Although smoking is the best-established risk factor for lung cancer, only five cohort studies presented smoking-adjusted risks out of all nine identified. Furthermore, only two studies explicitly reported the risk estimate for ex-drinkers who may have quit alcohol drinking after the development or diagnosis of the disease and have an apparently higher risk. CONCLUSION: We conclude that the epidemiologic evidence on the association between alcohol drinking and lung cancer risk remains insufficient in terms of both the number and methodological quality of studies among the Japanese population.     

Risk factors for breast cancer: epidemiological evidence from Japanese studies

Although our understanding of the etiology of breast cancer has improved, many well-known risk factors are not modifiable and present knowledge has proved insufficient to allow the disease to be overcome. Indeed, incidence and mortality among Japanese women have increased over the past three decades. Here, we review epidemiological evidence from our cohort and case-control studies among Japanese women in comparison with other published findings. Our studies confirm the important role of established factors derived primarily from Western populations, such as menstrual and reproductive factors, anthropometric factors, physical activity, and alcohol intake, in the development of breast cancer. In addition, we provide further evidence to better understand the role of traditional Japanese foods in the etiology of breast cancer. Our cohort study found that a higher intake of isoflavone and higher levels of plasma genistein, but not daidzein, were associated with a decreased risk of breast cancer. Our case-control studies reveal a dose-response pattern for these compounds; specifically, decreased risk as women move from "no" to "moderate" intake and leveling off thereafter. In addition, gene-environment interactions have been revealed in the effects of isoflavones. The evidence reviewed suggests that isoflavone has a protective effect against breast cancer in Asian populations. Conversely, our cohort study did not observe an inverse association between breast cancer risk and the intake of green tea and/or the plasma level of tea polyphenols, but we did find an association between increased risk and active and passive smoking. In conclusion, based on current knowledge, primary prevention according to individual lifestyle modification should focus on alcohol intake, weight control, physical activity, and tobacco smoking.     

Cigarette smoking and liver cancer risk: an evaluation based on a systematic review of epidemiologic evidence among Japanese

BACKGROUND: Emerging epidemiologic data suggest that cigarette smoking may increase the risk of primary liver cancer. We evaluated this association based on a systematic review of epidemiologic evidence among Japanese populations. METHODS: Original data were obtained from MEDLINE searches using PubMed, complemented with manual searches. The evaluation was performed in terms of the magnitude of association ('strong', 'moderate', 'weak' or 'no association') in each study and the strength of evidence ('convincing', 'probable', 'possible' or 'insufficient'), together with biological plausibility as previously done by the International Agency for Research on Cancer. RESULTS: A total of 12 cohort studies and 11 case-control studies were identified. Nine cohort studies (two with adjustment for hepatitis B and C virus infections and seven without it) reported weak to strong positive associations between smoking and liver cancer, with dose-response relationships shown in three studies. Five case-controls studies (three with the virus adjustment and two without it) demonstrated such positive associations, with a dose-response relationship shown in only one study, while in six case-control studies, the observed associations were judged to be of the lowest magnitude or inverse due to the lack of any dose-response relationship. CONCLUSION: We conclude that cigarette smoking 'probably' increases the risk of primary liver cancer among the Japanese. Potential confounding by hepatitis virus infection and virus-smoking interactions need to be addressed in future studies.     

Passive smoking exposure and female breast cancer mortality

BACKGROUND: Several studies have reported positive associations between environmental tobacco smoke (ETS) and increased risk of breast cancer. However, studies of active smoking and risk of breast cancer are equivocal and in general do not support a positive association. To try to resolve this paradox, we examined the association between breast cancer mortality and potential ETS exposure from spousal smoking in an American Cancer Society prospective study of U.S. adult women. METHODS: We assessed breast cancer death rates in a cohort of 146 488 never-smoking, single-marriage women who were cancer free at enrollment in 1982. Breast cancer death rates among women whose husbands smoked were compared with those among women married to men who had never smoked. Cox proportional hazards modeling was used to control for potential risk factors other than ETS exposure. RESULTS: After 12 years of follow-up, 669 cases of fatal breast cancer were observed in the cohort. Overall, we saw no association between exposure to ETS and death from breast cancer (rate ratio [RR] = 1.0; 95% confidence interval [CI] = 0.8-1.2). We did, however, find a small, not statistically significant increased risk of breast cancer mortality among women who were married before age 20 years to smokers (RR = 1. 2; 95% CI = 0.8-1.8). CONCLUSIONS: In contrast to the results of previous studies, this study found no association between exposure to ETS and female breast cancer mortality. The results of our study are particularly compelling because of its prospective design as compared with most earlier studies, the relatively large number of exposed women with breast cancer deaths, and the reporting of exposure by the spouse rather than by proxy.     

Dose-Dependent Associations between Wine Drinking and Breast Cancer Risk - Meta-Analysis Findings

Purpose: To investigate any potential association between wine and breast cancer risk. Materials and Methods: We quantitatively assessed associations by conducting a meta-analysis based on evidence from observational studies. In May 2014, we performed electronic searches in PubMed, EmBase and the Cochrane Library to identify studies examining the effect of wine drinking on breast cancer incidence. The relative risk (RR) or odds ratio (OR) were used to measure any such association. Results: The analysis was further stratified by confounding factors that could influence the results. A total of twenty-six studies (eight case-control and eighteen cohort studies) involving 21,149 cases were included in our meta-analysis. Our study demonstrated that wine drinking was associated with breast cancer risk. A 36% increase in breast cancer risk was observed across overall studies based on the highest versus lowest model, with a combined RR of 1.0059 (95%CI 0.97-1.05) in dose-response analysis. However, 5 g/d ethanol from wine seemed to have protective value from our non-linear model. Conclusions: Our findings indicate that wine drinking is associated with breast cancer risk in a dose-dependent manner. High consumption of wine contributes to breast cancer risk with protection exerted by low doses. Further investigations are needed for clarification.     

Alcohol drinking and colorectal cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

BACKGROUND: It remains unclear whether alcohol drinking is causally associated with colorectal cancer. On the basis of a systematic review of epidemiological evidence, we evaluated this association among the Japanese population, who may be more susceptible to alcohol-related diseases than Western populations. METHODS: Original data were obtained from searches of MEDLINE using PubMed, complemented with manual searches. The 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. RESULTS: We identified 5 cohort studies and 13 case-control studies. A moderate or strong positive association was observed between alcohol drinking and colon cancer risk in all large-scale cohort studies, with some showing a dose-response relation, and among several case-control studies. The risk of colon or colorectal cancer was increased even among moderate drinkers consuming <46 g of alcohol per day, levels at which no material increase in the risk was observed in a pooled analysis of Western studies. A positive association with rectal cancer was also reported, but it was less consistent, and the magnitude of the association was generally weaker compared with colon cancer. CONCLUSION: We conclude that alcohol drinking probably increases the risk of colorectal cancer among the Japanese population. More specifically, the association for the colon is probable, whereas that for the rectum is possible.     

Alcohol drinking and esophageal cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

Although alcohol drinking is considered as an important risk factor for esophageal cancer, the magnitude of the association might be varied among geographic areas. Therefore, we reviewed epidemiologic studies on the association between alcohol drinking and esophageal cancer among the Japanese population. Original data were obtained from MEDLINE, searched using PubMed or from searches of the Ichushi database, complemented with manual searches. Evaluation of associations was based on the strength of evidence ('convincing', 'probable', 'possible' or 'insufficient') and the magnitude of association ('strong', 'moderate', 'weak' or 'no association'), together with biological plausibility as previously evaluated by the International Agency of Research on Cancer. We identified four cohort studies and nine case-control studies. All cohort studies and case-control studies showed strong positive associations between esophageal cancer and alcohol drinking. All cohort studies and six case-control studies showed that alcohol drinking had the dose- or frequency-response relationships with esophageal cancer. In addition, four case-control studies showed that acetaldehyde dehydrogenase Glu504Lys polymorphism had strong effect modification with alcohol drinking. We conclude that there is convincing evidence that alcohol drinking increases the risk of esophageal cancer in the Japanese population.     

Alcohol drinking and total cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

BACKGROUND: We conducted a systematic review of epidemiological evidence to evaluate the association between alcohol drinking and total cancer risk among the Japanese population. METHODS: Original data were obtained from MEDLINE searches using PubMed or from searches of the Ichushi database, 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 of Research on Cancer. RESULTS: Of eight cohort studies identified, six studies, three of which included women, were subjected to evaluation. In men, all six studies showed a weak to moderate positive association between alcohol drinking and total cancer risk. While light drinking had little effect on total cancer risk, heavy drinking of more than 46-69 g of alcohol per day contributed to total cancer risk for most of these Japanese populations. However, no association was reported in women in any of the three studies. CONCLUSION: We conclude that there is convincing evidence that alcohol drinking increases the risk of total cancer in the Japanese population, specifically among heavy drinking men.     

Smoking and colorectal cancer: different effects by type of cigarettes?

Although smoking is suggested to be a risk factor for colorectal cancer, the evidence to date is conflicting and may be confounded. Moreover, the effect of tobacco smoke may vary by time since initiation, type of tobacco product, anatomic subsites, and among ethnic groups. Data were derived from two consecutive population-based case-control studies conducted among Caucasians, Japanese, Native Hawaiians, Filipinos, and Chinese in Hawaii, including 1,959 ethnicity-, sex-, and age-matched case-control pairs. A lifetime history of smoking for different tobacco products and information on other risk factors were obtained by in-person interviews. Odds ratios (OR) and corresponding 95% confidence intervals (95% CI) were estimated using conditional logistic regression models with adjustment for potential confounders. Subjects who ever smoked were at an increased risk of colorectal cancer compared with never smokers (OR, 1.23; 95% CI, 0.99-1.52 for men and OR, 1.27; 95% CI, 1.01-1.59 for women). Increasing quartiles of pack-years over all tobacco products showed a clear dose-dependent association in men [for the highest quartile, Q4 (>40 pack-years) versus never smokers: OR, 1.48; 95% CI, 1.12-1.96; P(trend) = 0.002]. The dose-response trend was also present in women [for the highest quartile, Q4 (>30 pack-years) versus never smokers: OR, 1.38; 95% CI, 0.91-1.95; P(trend) = 0.04] and each ethnic group. There was a suggestion of a difference in risk with type of tobacco product. Non-filtered cigarettes increased risk of both colon and rectal cancer [for Q4 versus never smokers: OR, 1.59; 95% CI, 1.15-2.21; P(trend) = 0.001 and OR, 1.84; 95% CI, 1.18-2.86; P(trend) = 0.02, respectively], whereas filtered cigarettes seemed to increase risk of rectal but not colon cancer (OR, 1.37; 95% CI, 0.88-2.13; P(trend) = 0.06 and OR, 1.05; 95% CI, 0.79-1.39; P(trend) = 0.98, respectively). The effect of smoking was not limited to the distant past, and accumulated pack-years of smoking seemed to be more important than the time in which smoking occurred. The data from this large study corroborate previous reports of a positive association between smoking and colorectal cancer and suggest that the association may vary by type of cigarette.     

Polymorphisms in XPC and ERCC2 genes, smoking and breast cancer risk

To evaluate the associations of breast cancer risk with polymorphisms in the XPC and XPD/ERCC2 DNA nucleotide excision repair genes, a case-control study nested within a prospective cohort of 14,274 women was conducted. Genotypes were characterized for 612 incident, invasive breast cancer cases and their 1:1 matched controls. The homozygous variant of a poly(AT) insertion/deletion polymorphism in intron 9 of the XPC gene (XPC-PAT+/+), was associated with breast cancer risk [odds ratio (OR) = 1.45, 95% confidence interval: 1.07-1.97], after adjustment for other breast cancer risk factors. The breast cancer risk associated with XPC-PAT+/+ did not differ by age at diagnosis. There was an indication of an interaction (p = 0.08) between the XPC-PAT+/+ genotype and cigarette smoking. Ever smokers with the XPC-PAT+/+ genotype were at elevated risk of breast cancer (OR = 1.56, CI: 0.95-2.58), but no differences were observed among never smokers. Analyses of the ERCC2 Lys751Gln polymorphism did not show an association with breast cancer risk, either overall or at younger ages. The results suggest that breast cancer risk is related to the XPC haplotype tagged by the XPC-PAT+/+ insertion-deletion polymorphism in intron 9. Further study of the XPC haplotypes and their interactions with smoking in relation to breast cancer risk is needed.     

Waterpipe Tobacco Smoking and Risk of Stomach Cancer: A Case-Control Study in Vietnamese Men

Objective: This study investigated the impacts of waterpipe tobacco (WTP) and cigarette smoking on stomach cancer development in Vietnamese men. Methods: A total of 80 stomach cancer cases and 146 controls were recruited in a hospital-based case-control study. Data on sociodemographic, anthropometric characteristics, tobacco smoking, and the dietary pattern was obtained based on a semi-quantitative food frequency and demographic lifestyle questionnaire; and venous anti-Helicobacter pylori IgG antibodies were tested by ELISA. Unconditional logistic regression analysis with adjustments for potential confounding was performed to estimate the association between target exposures and stomach cancer. Results: Compared to the never tobacco smokers, the risk of stomach cancer significantly increased among tobacco smokers (OR 2.95, 95%CI 1.26-6.90, p=0.013). Those who early started tobacco smoking before 26 years old had a high risk of SC (OR 3.04, 95%CI 1.29-7.20, p for trend=0.011). For types of tobacco, It was increased risk in exclusively cigarette smokers (OR 2.85, 95%CI 1.19-6.85, p=0.019) and in WPT smokers (OR 3.09, 95%CI 1.24-7.68, p=0.015). The daily frequency and longer duration of exclusively WPT or cigarette smoking tended to be significantly higher SC risk. Conclusions: The findings suggest that tobacco smoking, particularly water pipe tobacco smoking, dramatically and independently increased the risk of stomach cancer.     

Green tea, black tea and breast cancer risk: a meta-analysis of epidemiological studies

Experimental studies have shown that tea and tea polyphenols have anti-carcinogenic properties against breast cancer. A number of epidemiologic studies, both case-control and cohort in design, have examined the possible association between tea intake and breast cancer development in humans. This meta-analysis included 13 papers which examined populations in eight countries and provided data on consumption of either green tea or black tea, or both in relation to breast cancer risk. Summary odds ratios (ORs) for highest versus non/lowest tea consumption level were calculated based on fixed and random effects models. Heterogeneity between studies was examined via the Q statistics. For green tea, the combined results from the four studies indicated a reduced risk of breast cancer for highest versus non/lowest intake (OR = 0.78, 95% CI = 0.61-0.98). For black tea, conflicting results were observed in case-control versus cohort studies. The combined results from the eight case-control studies showed a minor inverse association between black tea consumption and risk of breast cancer (OR = 0.91, 95% CI = 0.84-0.98). This inverse association was stronger in hospital-based (OR = 0.77, 95% CI = 0.50-1.19) than population-based case-control studies (OR = 0.94, 95% CI = 0.81-1.09). Five cohort studies demonstrated a modest increase in risk associated with black tea intake (OR = 1.15, 95% CI = 1.02-1.31). The results of this meta-analysis indicate a lower risk for breast cancer with green tea consumption. Available data suggest a possible late-stage, promotional effect of black tea on breast carcinogenesis.     

Active and passive smoking and the risk of breast cancer in women aged 36-45 years: a population based case-control study in the UK

Active smoking has little or no effect on breast cancer risk but some investigators have suggested that passive smoking and its interaction with active smoking may be associated with an increased risk. In a population based case-control study of breast cancer in women aged 36-45 years at diagnosis, information on active smoking, passive smoking in the home, and other factors, was collected at interview from 639 cases and 640 controls. Women were categorised jointly by their active and passive smoking exposure. Among never smoking controls, women who also reported no passive smoking exposure were significantly more likely to be nulliparous and to be recent users of oral contraceptives. Among those never exposed to passive smoking, there was no significant association between active smoking and breast cancer, relative risk (RR) of 1.12 (95% confidence interval (CI) 0.72-1.73) for past smokers and RR of 1.19 (95% CI 0.72-1.95) for current smokers, nor was there an association with age started, duration or intensity of active smoking. Compared with women who were never active nor passive smokers, there was no significant association between passive smoking in the home and breast cancer risk in never smokers, RR of 0.89 (95% CI 0.64-1.25), in past smokers, RR of 1.09 (95% CI 0.75-1.56), or in current smokers, RR of 0.93 (95% CI 0.67-1.30). There was no trend with increasing duration of passive smoking and there was no heterogeneity among any of the subgroups examined. In this study, there was no evidence of an association between either active smoking or passive smoking in the home and risk of breast cancer.     

Active and passive smoking and breast cancer risk in middle-aged Japanese women

To examine the hypothesis that tobacco smoke is associated with the risk of female breast cancer, we estimated the relative risks of active and passive smoke in middle-aged Japanese women in a population-based prospective study. The cohort consisted of residents in 4 public health center areas, aged 40 to 59 years. A self-administered questionnaire survey was conducted in 1990. This analysis included 21,805 subjects, 180 of whom had developed breast cancer by December 31, 1999. When the reference was defined as never-active smokers without passive smoking, adjusted relative risks (RRs) were 1.9 (95% confidence interval [CI] = 1.0-3.6) in current active smokers, 1.2 (95% CI = 0.4-4.0) in ex-active smokers and 1.2 (95% CI = 0.8-1.6) in never-active smokers with passive smoking. The elevated risk for ever-smokers was clearly observed in premenopausal women at baseline (RR = 3.9, 95% CI = 1.5-9.9) but not in postmenopausal women (RR = 1.1, 95% CI = 0.5-2.5). In never-active smokers, the adjusted RR for passive smoking, residential or occupational/public tobacco smoke exposure was 1.1 (95% CI = 0.8-1.6). In premenopausal women, passive smoking increased the risk (RR = 2.6; 95% CI = 1.3-5.2) but not in postmenopausal women (RR = 0.7; 95% CI = 0.4-1.0). We conclude that tobacco smoking increases the risk of female breast cancer in premenopausal women.