Breast cancer and active and passive smoking: the role of the N-acetyltransferase 2 genotype

Lifetime personal cigarette smoking and risk of young-onset breast cancer by subtype among non-Hispanic Black and White women in the Young Women's Health History Study

PURPOSE

To evaluate the association between lifetime personal cigarette smoking and young-onset breast cancer (YOBC; diagnosed <50 years of age) risk overall and by breast cancer (BC) subtype, and whether risk varies by race or socioeconomic position (SEP).

METHODS

Data are from the Young Women's Health History Study (YWHHS), a population-based case-control study of non-Hispanic Black (NHB) and White (NHW) women, ages 20-49 years (n = 1812 cases, n = 1381 controls) in the Los Angeles County and Metropolitan Detroit Surveillance, Epidemiology, and End Results (SEER) registry areas, 2010-2015. Lifetime personal cigarette smoking characteristics and YOBC risk by subtype were examined using sample-weighted, multivariable-adjusted polytomous logistic regression.

RESULTS

YOBC risk associated with ever versus never smoking differed by subtype (Pheterogeneity = 0.01) with risk significantly increased for Luminal A (adjusted odds ratio [aOR] 1.34; 95% confidence interval [CI] 1.06-1.68) and HER2-type (aOR 1.97; 95% CI 1.23-3.16), and no association with Luminal B or Triple Negative subtypes. Additionally, ≥30 years since smoking initiation (versus never) was statistically significantly associated with an increased risk of Luminal A (aOR 1.55; 95% CI 1.07-2.26) and HER2-type YOBC (aOR 2.77; 95% CI 1.32-5.79), but not other subtypes. In addition, among parous women, smoking initiated before first full-term pregnancy (versus never) was significantly associated with an increased risk of Luminal A YOBC (aOR 1.45; 95% CI 1.11-1.89). We observed little evidence for interactions by race and SEP.

CONCLUSION

Findings confirm prior reports of a positive association between cigarette smoking and Luminal A YOBC and identify a novel association between smoking and HER2-type YOBC.

Recent insights into cigarette smoking as a lifestyle risk factor for breast cancer

There have been many cohort studies published reviewing the epidemiological evidence that links breast cancer to cigarette smoking, yet the underlying mechanisms are largely unknown and research studies are few and incomplete. Although cohort studies are important in establishing a connection between breast cancer and cigarette smoking, basic science research is necessary to prove the relationship and to highlight potential interventions and drug targets that can be used to manage the disease. This subject has been controversial for many decades; however, there has been a recent resurgence in interest because of the widespread acknowledgment of the role lifestyle choices play in cancer development and progression. This review will detail the current statistics associated with cigarette smoking and discuss recent cohort and basic research studies that highlight the association of cigarette smoking and breast cancer initiation and progression.

Estimating the Economic Impact of Secondhand Smoke on the Health of a Community

Purpose.

This study provides a model to estimate the health-related costs of secondhand smoke exposure at a community level.

Model Development.

Costs of secondhand smoke–related mortality and morbidity were estimated using national attributable risk values for diseases that are causally related to secondhand smoke exposure for adults and children. Estimated costs included ambulatory care costs, hospital inpatient costs, and loss of life costs based on vital statistics, hospital discharge data, and census data.

Application of the Model.

The model was used to estimate health-related costs estimates of secondhand smoke exposure for Marion County, Indiana. Attributable risk values were applied to the number of deaths and hospital discharges to determine the number of individuals impacted by secondhand smoke exposure.

Results.

The overall cost of health care and premature loss of life attributed to secondhand smoke for the study county was estimated to be $53.9 million in 2000—$10.5 million in health care costs and $20.3 million in loss of life for children compared with $6.2 million in health care costs and $16.9 million in loss of life for adults. This amounted to $62.68 per capita.

Conclusions.

This method may be replicated in other counties to provide data needed to educate the public and community leaders about the health effects and costs of secondhand smoke exposure.

Environmental tobacco smoke exposure and risk of breast cancer in nonsmoking women. An updated review and meta-analysis

CONTEXT

In 2006, we reviewed the evidence on environmental tobacco smoke (ETS) and breast cancer in nonsmoking women. Since then various studies and reviews have been published but opinion remains divided.

OBJECTIVE

To provide an updated review.

METHODS

We extracted study details, derived relative risk (RR) estimates with confidence intervals (CIs) for various ETS exposure indices, and conducted meta-analyses.

RESULTS

The update increased the number of studies from 22 to 47. Using an index for each study most closely equivalent to "spouse ever smoked", a weak but significant association was seen (random-effects RR = 1.15, 95% CI = 1.07-1.23). However, the estimates were heterogeneous: higher for Asian studies than for North American or European studies, higher for studies adjusting for fewer potential confounding variables, and close to 1.0 for prospective studies, regardless of whether or not they asked detailed questions on ETS exposure. The RR for eight prospective studies asking detailed questions was 1.003, 95% CI = 0.96-1.05. Risk was increased in premenopausal women (RR = 1.36, 95% CI = 1.15-1.60), but not postmenopausal women. Dose-response findings were similarly heterogeneous. No significant increase was seen for childhood or workplace exposure, but an increase was seen for total exposure (RR = 1.22, 95% CI = 1.09-1.37).

CONCLUSIONS

Increases mainly derived from case-control studies are prone to recall bias. Study weaknesses and possible publication bias limit interpretation. Considering also the weak association of smoking with breast cancer, and the much lower exposures from ETS than from smoking, our analyses do not clearly demonstrate that ETS exposure increases risk of breast cancer in nonsmokers. More research is needed.

Active cigarette smoking and the risk of breast cancer at the level of N-acetyltransferase 2 (NAT2) gene polymorphisms

The aim of our study was to assess the correlation between the tobacco exposure and NAT2 gene (rs1041983 C/T, rs1801280 T/C, rs1799930 G/A) polymorphisms in association with breast cancer development. We wanted to determine the prognostic clinical importance of these polymorphisms in association with smoking and breast cancer. For the detection of possible association between smoking, NAT2 gene polymorphisms, and the risk of breast cancer, we designed a case-controlled study with 198 patients enrolled, 98 breast cancer patients and 100 healthy controls. Ten milliliters of peripheral blood from the cubital vein was withdrawn from every patient. The HRM (high resolution melting) analysis was used for the detection of three abovementioned NAT2 gene polymorphisms. When comparing a group of women smoking more than 5 cigarettes a day with the patients smoking fewer than 5 cigarettes a day, we found out that if women were the carriers of aberrant AA genotype for rs1799930, the first group of women had higher risk of breast carcinoma than the second group. If patients were the carriers of aberrant TT genotype for rs1041983, for rs1801280CC genotype, and rs1799930AA genotype and they smoked more than 5 cigarettes a day, they had higher risk of malignant breast disease than never-smoking women. Our results confirm the hypothesis that NAT2 gene polymorphisms (rs1041983 C/T, rs1801280 T/C, and rs1799930 G/A) in association with long-period active smoking could be the possible individual risk-predicting factors for breast cancer development in the population of Slovak women.

N-acetyltransferase 2 polymorphism and breast cancer risk with smoking: a case control study in Japanese women

BACKGROUND

Recent studies have suggested that the association between smoking and breast cancer risk might be modified by polymorphisms in the N-acetyltransferase 2 gene (NAT2). Most of these studies were conducted in Western countries, with few reports from East Asia.

METHODS

We conducted a case-control study of 511 breast cancer cases and 527 unmatched healthy controls from December 2010 to November 2011 in Japan. Unconditional logistic regression was used to analyze the association of smoking with breast cancer risk stratified by NAT2 phenotype.

RESULTS

In this population, 11 % of the cases and 10 % of the controls were classified as a slow acetylator phenotype. Compared to never smokers, current smokers had an increased breast cancer risk in multivariate analysis [odds ratio (OR) = 2.27, 95 % confidence interval (95 %CI) = 1.38-3.82]. Subgroup analyses of menopausal status indicated the same tendency. Subgroup analyses of NAT2 phenotype, the ORs in both of rapid and slow acetylator phenotype subgroups were comparable, and no interactions were observed between smoking status and NAT2 phenotype (p = 0.97). A dose-dependent effect of smoking on breast cancer risk was seen for the rapid acetylator phenotype, but not for the slow acetylator phenotype.

CONCLUSION

Given the high frequency of the rapid acetylator phenotype, these results show that smoking is a risk factor for breast cancer among most Japanese women. It may be of little significance to identify the NAT2 phenotype in the Japanese population.

Landscape of NAT2 polymorphisms among breast cancer

PURPOSE

The prevalence of phenotypes of Arylamine N-acetyltransferase-2(NAT2) gene (i.e. fast, intermediate and slow acetylators) among ethnic groups, as well as the association studies regarding NAT2 polymorphisms and risk of breast cancer produced inconsistent results. This meta-analysis aimed to clarify whether the selected NAT2 phenotypes have an effect on the susceptibility to breast cancer.

METHODS

After aggregating the frequencies of fast, intermediate and slow phenotypes of NAT2 in breast cancer subjects, the odds ratio and relevant 95% confidence intervals were examined using combined data from all published 36 articles.

RESULTS

Overall, our results did not produce statistical significance for the proposed association, suggesting that there is no association between the selected phenotypes of NAT2 polymorphisms and breast cancer. In subgroup analyses, it was revealed that, as compared with the fast phenotype, intermediate acetylator is protective of the vulnerable White population to breast cancer. In addition, an obvious ethnic/geographic difference was found in the prevalence of fast, intermediate and slow acetylators among world-wide populations.

CONCLUSIONS

Although ethnic and geographic differences in NAT2 polymorphisms were present, this was not associated with the risk of breast cancer in general. Intermediate acetylator is protective for particular ethnic groups, a finding which should be carefully viewed and confirmed in the future studies.

Passive smoking exposure from partners as a risk factor for ER+/PR+ double positive breast cancer in never-smoking Chinese urban women: a hospital-based matched case control study

Background

The relationship between passive smoking exposure (PSE) and breast cancer risk is of major interest.

Objective

To evaluate the relationship between PSE from partners and breast cancer risk stratified by hormone-receptor (HR) status in Chinese urban women population.

Design

Hospital-based matched case control study.

Setting

Chinese urban breast cancer patients without current or previous active smoking history in China Medical University 1st Hospital, Liaoning Province, China between Jan 2009 and Nov 2009.

Patients

Each breast cancer patient was matched 1∶1 with healthy controls by gender and age (±2 years) from the same hospital.

Measurements

The authors used unconditional logistic regression analyses to estimate odds ratio for women with PSE from partners and breast cancer risk.

Results

312 pairs were included in the study. Women who endured PSE had significantly increased risk of breast cancer (adjusted OR: 1.46; 95% CI: 1.05–2.03; P = 0.027), comparing with unexposed women. Women who exposed to >5 cigarettes/day also had significant increased risk (adjusted OR: 1.99; 95% CI: 1.28–3.10; P = 0.002), as were women exposed to passive smoke for 16–25 years (adjusted OR: 1.87 95% CI: 1.22–2.86; P = 0.004), and those exposed to > 4 pack-years (adjusted OR: 1.71 95% CI: 1.17–2.50; P = 0.004). Similar trends were significant for estrogen receptor (ER)/progesterone receptor (PR) double positive subgroup(adjusted OR: 1.71; 2.20; 1.99; 1.92, respectively), but not for ER+/PR−, ER−/PR+, or ER−/PR− subgroups.

Limitations

limitations of the hospital-based retrospective study, lack of information on entire lifetime PSE and low statistical power.

Conclusions

Our findings provide further evidence that PSE from partners contributes to increased risk of breast cancer, especially for ER/PR double positive breast cancer, in Chinese urban women.

Active and passive cigarette smoking and breast cancer risk: results from the EPIC cohort

Recent cohort studies suggest that increased breast cancer risks were associated with longer smoking duration, higher pack-years and a dose-response relationship with increasing pack-years of smoking between menarche and first full-term pregnancy (FFTP). Studies with comprehensive quantitative life-time measures of passive smoking suggest an association between passive smoking dose and breast cancer risk. We conducted a study within the European Prospective Investigation into Cancer and Nutrition to examine the association between passive and active smoking and risk of invasive breast cancer and possible effect modification by known breast cancer risk factors. Among the 322,988 women eligible for the study, 9,822 developed breast cancer (183,608 women with passive smoking information including 6,264 cases). When compared to women who never smoked and were not being exposed to passive smoking at home or work at the time of study registration, current, former and currently exposed passive smokers were at increased risk of breast cancer (hazard ratios (HR) [95% confidence interval (CI)] 1.16 [1.05-1.28], 1.14 [1.04-1.25] and 1.10 [1.01-1.20], respectively). Analyses exploring associations in different periods of life showed the most important increase in risk with pack-years from menarche to FFTP (1.73 [1.29-2.32] for every increase of 20 pack-years) while pack-years smoked after menopause were associated with a significant decrease in breast cancer risk (HR = 0.53, 95% CI: 0.34-0.82 for every increase of 20 pack-years). Our results provide an important replication, in the largest cohort to date, that smoking (passively or actively) increases breast cancer risk and that smoking between menarche and FFTP is particularly deleterious.

Smoking and breast cancer

The potential role of smoking in breast cancer risk has been the subject of over 100 publications, numerous scientific reviews, and animated debate. Tobacco exposure is a well-established cause of lung cancer, and is thought to account for nearly one third of all cancer deaths. Tobacco smoke contains thousands of chemicals, many of which are known to be mammary carcinogens. Although not initially thought to be a tobacco-related cancer, over the last several decades evidence has been accumulating on the role of both active smoking and secondhand smoking in the etiology of breast cancer. The human health evidence has been systematically evaluated not only by several independent researchers but also by several expert agency panels including those of the U.S. Surgeon General, the International Agency for Research on Cancer, the California Environmental Protection Agency, and a coalition of Canadian health agencies. Although the assessments have varied with time and across reviewers, the most recent weight of the evidence has suggested a potentially casual role for active smoking and breast cancer, particularly for long-term heavy smoking and smoking initiation at an early age. The role of secondhand smoking and breast cancer is less clear, although there has been some suggestion for an increased risk for premenopausal breast cancer. Recent studies evaluating the possible modifying role of polymorphisms in genes involved in the metabolism of tobacco products, particularly NAT2, have contributed another dimension to these assessments, although to date that evidence remains equivocal.

Smoking and survival after breast cancer diagnosis: a prospective observational study and systematic review

The association of smoking with outcomes following breast cancer prognosis is not well understood. In a cohort study called Life After Cancer Epidemiology (LACE), 2,265 women diagnosed with breast cancer were followed for a median of 12 years. We used multivariable proportional-hazards models to determine whether smoking, assessed approximately two years post-diagnosis, was associated with risk of death among these women. We also undertook a systematic review of all cohort studies to date that have examined the association between smoking and breast cancer mortality. Compared with never smokers, women who were current smokers had a twofold higher rate of dying from breast cancer [hazard ratio (HR) = 2.01, 95 % confidence interval (CI) 1.27-3.18] and an approximately fourfold higher rate of dying from competing (non-breast cancer) causes (HR = 3.84, 95 % CI 2.50-5.89). Among seven studies that met the inclusion criteria in the systematic review, three studies and our own reported significantly increased risk of breast cancer death with current smoking. We found little evidence of an association between former smoking and breast cancer mortality (HR = 1.24, 95 % CI 0.94-1.64). Consistent with findings from our prospective observational study, the systematic review of seven additional studies indicates positive association of current smoking with breast cancer mortality, but weak association with former smoking. Women who smoke following breast cancer diagnosis and treatment are at higher risk of death both from breast cancer and other causes.

Passive cigarette smoke exposure during various periods of life, genetic variants, and breast cancer risk among never smokers

The association between passive cigarette smoke exposure and breast cancer risk is inconclusive and may be modified by genotype. The authors investigated lifetime passive cigarette smoke exposures, 36 variants in 12 carcinogen-metabolizing genes, and breast cancer risk among Ontario, Canada, women who had never smoked (2003-2004). DNA (saliva) was available for 920 breast cancer cases and 960 controls. Detailed information about passive smoke exposure was collected for multiple age periods (childhood, teenage years, and adulthood) and environments (home, work, and social). Adjusted odds ratios and 95% confidence intervals were estimated by multivariable logistic regression, and statistical interactions were assessed using the likelihood ratio test. Among postmenopausal women, most associations between passive smoke and breast cancer risk were null, whereas among premenopausal women, nonsignificant positive associations were observed. Significant interactions were observed between certain types of passive smoke exposure and genetic variants in CYP2E1, NAT2, and UGT1A7. While these interactions were statistically significant, the magnitudes of the effect estimates were not consistent or easily interpretable, suggesting that they were perhaps due to chance. Although the results of this study were largely null, it is possible that premenopausal women exposed to passive smoke or carrying certain genetic variants may be at higher risk of breast cancer.

Perspectives of breast cancer etiology: synergistic interaction between smoking and exogenous hormone use

To explore breast cancer etiology, literature was searched using Medline. We explored the 1) plausibility of smoking in breast carcinogenesis; 2) physiological properties, susceptibility windows, and exposure timing of breast cells; 3) role of exogenous hormones in breast carcinogenesis; 4) biological mechanism of synergistic interactions between smoking and exogenous hormones in breast carcinogenesis; and 5) evidence from epidemiologic studies and the fitted secular trend between smoking rate, exogenous hormone use, and breast cancer incidence in past decades. We deduced that exogenous hormone use per se is not a significant cause and its association with breast cancer is distorted by chronic exposure to environmental carcinogens, especially smoking. We hypothesize that smoking is one of the causes of breast cancer and that this causality is strengthened by synergistic interaction between smoking and exogenous hormone use. Physicians should be cautious of prescribing exogenous hormones for those with chronic exposure to environmental carcinogens to prevent breast cancer.

Lifetime tobacco smoke exposure and breast cancer incidence

PURPOSE

We analyzed data from a case-control study to assess the association between lifetime tobacco smoke exposure and breast cancer incidence.

METHODS

Incident breast cancer cases were identified in the Massachusetts Cancer Registry and population controls were sampled from state Medicare lists and driver's license rosters. Demographic, lifestyle, medical history, reproductive history, and passive and active smoking exposure variables were assessed by telephone interview. We defined passive and active tobacco smoke exposure categories reflective of lifetime exposure patterns, and compared breast cancer risk among these groups while adjusting for age, body mass index, menopausal status, parity, alcohol consumption, and family history of breast cancer. We also adjusted passive smoking associations for active smoking status and vice versa.

RESULTS

We observed no association between ever being passively exposed to tobacco smoke and risk of incident breast cancer (adjusted OR: 1.2; 95% CI: 0.8, 1.8) nor between active smoking and breast cancer (adjusted OR for [23 pack-years compared to nonsmokers: 0.9; 95% CI: 0.7, 1.3). Null effects persisted in finer categorizations of active and passive exposure.

CONCLUSIONS

We observed no causal associations between active or passive tobacco smoke exposures and incident breast cancer, consistent with results from most prospective cohort studies.

History of smoking is associated with younger age at diagnosis of breast cancer

Smoking tobacco has been associated with incidence, response and outcomes after treatment of some cancers. We hypothesized that tobacco use could result in an observable effect on breast cancer stage and characteristics at diagnosis. There were 6,000 patients with Tis-4, N0-3 breast cancers who presented to a comprehensive cancer center at initial diagnosis between 1970 and 2006. Patients were included who had a known smoking history, and subdivided into any tobacco use 2683 (45%) or never tobacco use 3317 (55%). Analyses were performed to evaluate the association of smoking with clinical, pathologic and treatment-related factors at cancer presentation. Median age at diagnosis for all breast cancers was 55 years, for nonsmokers was 56 years, for any smoking history was 55 years, and the subgroup of current smokers was 52 years. The difference in median age for current smokers versus nonsmokers was statistically significant (p < 0.0001). The probability of age <55 years at breast cancer diagnosis for any smoking history compared to nonsmokers was 1.2 for white patients (p < 0.0003) but 0.81 for black patients (p = 0.25). There was no statistically significant association between smoking and T stage, N stage, ER/PR status, or Her-2/neu status, although smokers were less likely to utilize breast-conserving treatment. Smoking was associated with a younger age at diagnosis and lower utilization of breast conservation, and observed in the subgroup of white patients but not black patients. Further efforts to clarify potential reasons for any racial differences and lower utilization of breast conservation with smoking are warranted.

NAT2 polymorphisms combining with smoking associated with breast cancer susceptibility: a meta-analysis

To derive a more precise estimation of the relationship between the slow or rapid acetylation resulting from N-acetyltransferase 2 (NAT2) polymorphisms and breast cancer risk, a meta-analysis was performed. PubMed, Medline, Embase, and Web of Science were searched. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess strength of association. The pooled ORs were performed for slow versus rapid acetylation genotypes. A total of 26 studies including 9,215 cases and 10,443 controls were included in the meta-analysis. Overall, no significantly elevated breast cancer risk was associated with NAT2 slow genotypes when all studies were pooled into the meta-analysis (OR = 1.026, 95% CI = 0.968-1.087). In the subgroup analysis by ethnicity, increased risks were not found for either Caucasians (OR = 1.001, 95% CI = 0.938-1.068) or Asians (OR = 1.155, 95% CI = 0.886-1.506). When stratified by study design, statistically significantly elevated risk associated with NAT2 slow genotypes was only found among hospital-based studies (OR = 1.178, 95% CI = 1.037-1.339). In the subgroup analysis by menopausal status, no statistically significantly increased risk was found in either premenopausal (OR = 1.053, 95% CI = 0.886-1.252) or postmenopausal women (OR = 0.965, 95% CI = 0.844-1.104). When stratified by cumulative smoking exposure, in the subgroup of smokers with high pack-years, NAT2 slow genotypes were significantly associated with increased breast cancer risk (OR = 1.400, 95% CI = 1.099-1.784). In conclusion, this meta-analysis suggested that there is overall lack of association between NAT2 genotypes and breast cancer risk, however, NAT2 polymorphisms when combining with heavy smoking history may contribute to breast cancer susceptibility.

Passive smoking and risk of breast cancer in the California teachers study

BACKGROUND

Although recent reviews have suggested active smoking to be a risk factor for breast cancer, the association with passive smoke exposure remains controversial. This risk association was explored in a large prospective study of women, the California Teachers Study.

METHODS

Detailed lifetime information on passive smoke exposure by setting (home, work, or social) and by age of exposure was collected in 1997 from 57,523 women who were lifetime nonsmokers and had no history of breast cancer. In the ensuing decade, a total of 1,754 women were diagnosed with invasive breast cancer. Cox proportional hazards models were fit to estimate hazard ratios (HR) and 95% confidence intervals (95% CI) associated with several lifetime passive smoke exposure metrics.

RESULTS

For all breast cancer, measures of higher lifetime passive smoking intensity and duration were associated with nonstatistically significant HRs of 1.11 to 1.14. For postmenopausal women, HRs for lifetime low, medium, and high cumulative exposure were 1.17 (95% CI, 0.91-1.49), 1.19 (95% CI, 0.93-1.53), and 1.26 (95% CI, 0.99-1.60). For women exposed in adulthood (age > or =20 years), risk was elevated at the highest level of cumulative exposure (HR, 1.18; 95% CI, 1.00-1.40), primarily among postmenopausal women (HR, 1.25; 95% CI, 1.01-1.56). A statistically significant dose response was detected when analysis was restricted to women with moderate to high levels of passive smoke exposure.

CONCLUSION

These results suggest that cumulative exposures to high levels of sidestream smoke may increase breast cancer risk among postmenopausal women who themselves have never smoked tobacco products.

N-acetyltransferase 2 genotype modification of active cigarette smoking on breast cancer risk among hispanic and non-hispanic white women

While it has been demonstrated that cigarette smoke contains aromatic and heterocyclic amines that initiate carcinogenesis, the association between cigarette smoking and breast cancer remains controversial. N-acetyltransferase 2 (NAT2) catalyzes arylamine carcinogen biotransformation and NAT2 genetic polymorphisms may contribute to differential susceptibility to breast cancer. We tested whether NAT2 modified the association between cigarette smoking and breast cancer risk in a population-based study of Hispanic and non-Hispanic white women in the Southwest United States. Data were available for cigarette smoking and NAT2 polymorphisms for 717 cases (Hispanic, 251 and non-Hispanic white, 466) and 735 controls (Hispanic, 245 and non-Hispanic white, 490). NAT2 genotypes were translated into rapid, intermediate, slow, or very slow acetylator phenotypes. Odds ratios (ORs) and 95% confidence intervals (95% CIs) for the joint association of NAT2 with smoking on breast cancer risk were estimated using logistic regression. Non-Hispanic white women were more likely (p < 0.001) than Hispanic women to have a slow (41.7 vs. 33.5%) or very slow (19.0 vs. 11.1%) acetylator status and less likely to have rapid/intermediate phenotypes (39.2 vs. 54.4%). Breast cancer risk was significantly increased in non-Hispanic white women with a very slow acetylator phenotype who smoked: ever versus never (OR, 2.57; 95% CI, 1.49-4.41), never versus former (OR, 2.69; 95% CI, 1.41-5.17) or current (OR, 2.46; 95% CI, 1.07-5.65), and 16 + pack-years (OR, 2.29; 95% CI, 1.16-4.51). Results for Hispanic women were not statistically significant. These findings support smoking as a risk factor for breast cancer among non-Hispanic white women with very slow NAT2 acetylator phenotype.

Differences between human slow N-acetyltransferase 2 alleles in levels of 4-aminobiphenyl-induced DNA adducts and mutations

Aromatic amines such as 4-aminobiphenyl (ABP) require biotransformation to exert their carcinogenic effects. Genetic polymorphisms in biotransformation enzymes such as N-acetyltransferase 2 (NAT2) may modify cancer risk following exposure. Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human cytochrome P4501A1 (CYP1A1) and a single copy of either NAT2*4 (rapid acetylator), NAT2*5B (common Caucasian slow acetylator), or NAT2*7B (common Asian slow acetylator) alleles (haplotypes) were treated with ABP to test the effect of NAT2 polymorphisms on DNA adduct formation and mutagenesis. ABP N-acetyltransferase catalytic activities were detectable only in cell lines transfected with NAT2 and were highest in cells transfected with NAT2*4, lower in cells transfected with NAT2*7B, and lowest in cells transfected with NAT2*5B. Following ABP treatment, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) was the primary adduct formed. Cells transfected with both CYP1A1 and NAT2*4 showed the highest concentration-dependent cytotoxicity, hypoxanthine phosphoribosyl transferase (hprt) mutants, and dG-C8-ABP adducts. Cells transfected with CYP1A1 and NAT2*7B showed lower levels of cytotoxicity, hprt mutagenesis, and dG-C8-ABP adducts. Cells transfected with CYP1A1 only or cells transfected with both CYP1A1 and NAT2*5B did not induce cytotoxicity, hprt mutagenesis or dG-C8-ABP adducts. ABP-DNA adduct levels correlated very highly (r>0.96) with ABP-induced hprt mutant levels following each treatment. The results of the present study suggest that investigations of NAT2 genotype or phenotype associations with disease or toxicity could be more precise and reproducible if heterogeneity within the "slow" NAT2 acetylator phenotype is considered and incorporated into the study design.

ArylamineN-Acetyltransferases: What We Learn from Genes and Genomes

Arylamine N-acetyltransferases (NATs) are phase II xenobiotic metabolizing enzymes, catalyzing acetyl-CoA-dependent N- and O-acetylation reactions. All NATs have a conserved cysteine protease-like Cys-His-Asp catalytic triad inside their active site cleft. Other residues determine substrate specificity, while the C-terminus may control hydrolysis of acetyl-CoA during acetyltransfer. Prokaryotic NAT-like coding sequences are found in >30 bacterial genomes, including representatives of Actinobacteria, Firmicutes and Proteobacteria. Of special interest are the nat genes of TB-causing Mycobacteria, since their protein products inactivate the anti-tubercular drug isoniazid. Targeted inactivation of mycobacterial nat leads to impaired mycolic acid synthesis, cell wall damage and growth retardation. In eukaryotes, genes for NAT are found in the genomes of certain fungi and all examined vertebrates, with the exception of canids. Humans have two NAT isoenzymes, encoded by highly polymorphic genes on chromosome 8p22. Syntenic regions in rodent genomes harbour two Nat loci, which are functionally equivalent to the human NAT genes, as well as an adjacent third locus with no known function. Vertebrate genes for NAT invariably have a complex structure, with one or more non-coding exons located upstream of a single, intronless coding region. Ubiquitously expressed transcripts of human NAT1 and its orthologue, murine Nat2, are initiated from promoters with conserved Sp1 elements. However, in humans, additional tissue-specific NAT transcripts may be expressed from alternative promoters and subjected to differential splicing. Laboratory animals have been widely used as models to study the effects of NAT polymorphism. Recently generated knockout mice have normal phenotypes, suggesting no crucial endogenous role for NAT. However, these strains will be useful for understanding the involvement of NAT in carcinogenesis, an area extensively investigated by epidemiologists, often with ambiguous results.

Passive smoking and breast cancer in never smokers: prospective study and meta-analysis

BACKGROUND

Active smoking has little or no effect on women's risk of developing breast cancer, but it has been suggested that passive exposure to tobacco smoke may increase this risk among women who have never smoked.

OBJECTIVE

To evaluate the possible relationship between passive smoking and breast cancer risk within the Million Women Study, a large UK prospective study, and to report a meta-analysis of published results.

METHODS

In the large prospective study, 224 917 never smokers who completed a questionnaire that asked women whether their parents had smoked and if their current partner smoked were followed up for an average of 3.5 years for incident breast cancer. In the meta-analysis, studies that had recorded exposure information prospectively and retrospectively were considered separately. Main outcome measures Adjusted relative risk of breast cancer in never smokers who were passively exposed to tobacco smoke at various ages compared with never smokers with no such exposure.

RESULTS

In the prospective study, 2518 incident invasive breast cancers occurred during follow-up and the adjusted relative risk of breast cancer for passive exposure either as a child or as an adult vs neither exposure was 0.98 (95% CI 0.88-1.09); results were similarly null for childhood exposure (0.98, 0.88-1.08) and adult exposure (1.02, 0.89-1.16) separately. We identified seven other studies with prospectively recorded exposure data; when results of all eight studies were combined (including 5743 never smokers with breast cancer), the aggregate relative risk was 0.99 (0.93-1.05) for any passive exposure. The aggregate findings differed substantially (P = 0.0002) between these 8 studies and 17 other studies with retrospectively recorded information (including 5696 never smokers with breast cancer).

CONCLUSIONS

Aggregate results from studies with prospectively reported information show that the incidence of breast cancer is similar in women who did and did not report passive exposure to tobacco smoke either as a child or as an adult. The aggregate findings from the retrospective studies may have been distorted by some women becoming more likely to report past exposures because they knew that they had breast cancer.

Effects of tobacco smoke condensate on estrogen receptor-alpha gene expression and activity

Metallo-estrogens are a new class of potent environmental estrogens. This study investigates whether tobacco smoke condensate (TSC), which contains metals and metalloids, elicits estrogen-like effects at environmentally relevant doses. Treatment of human breast cancer cells, MCF-7, with 40 microg/ml TSC resulted in a 2.5-fold stimulation of cell growth. TSC decreased the concentration of estrogen receptor (ER)-alpha protein and mRNA (63 and 62%, respectively), and increased the expression of the estrogen-regulated genes, progesterone receptor and pS2 (5- and 2-fold, respectively). In addition, TSC activated ER-alpha in COS-1 or CHO cells transiently transfected with wild-type ER-alpha and an ERE-CAT or an ERE-luciferase reporter gene (11- and 6-fold, respectively). TSC also activated a chimeric receptor (GAL-ER) containing the hormone binding domain of ER-alpha (3.5-fold). It blocked the binding of estradiol to the receptor without altering the affinity of estradiol (K(d) = 2.2-6.8 x 10(-10) m). Transfection assays with ER-alpha mutants identified C381, C447, H524, N532, E523, and D538 in the hormone binding domain as important for activation by TSC. In ovariectomized rats, low doses of TSC [10 or 20 mg/kg body weight (bw)] increased uterine wet weight (1.7- and 2.1-fold), and induced the expression of progesterone receptor and complement C3 in the uterus (2- and 26-fold) and mammary gland (4.4- and 15-fold). Both the in vitro and in vivo TSC effects were blocked by the antiestrogen ICI 182,780, suggesting the involvement of ER. Collectively, these results provide strong evidence that low doses of TSC, acting through the hormone binding domain, exert estrogen-like effects in cell culture and animals.

A meta-analysis of the association of N-acetyltransferase 2 gene (NAT2) variants with breast cancer

The N-acetyltransferase 2 gene (NAT2) product is an enzyme important in carcinogen metabolism via activation and detoxification pathways. Therefore, NAT2 variants may represent underlying susceptibility to breast cancer. Because a number of studies of the association of NAT2 with breast cancer have been published, the authors performed a meta-analysis. They extracted all relevant data to examine evidence for a main effect (i.e., the effect in a model that does not include any interactions) of NAT2 phenotype and genotype on breast cancer risk. They summarized the evidence for modification by smoking and meat intake, sources of exposure to aromatic and heterocyclic amines, respectively, which are metabolized by NAT2. The authors identified seven studies that measured NAT2 phenotype and 20 studies that deduced phenotype via genotyping. They found no evidence for heterogeneity (Cochran's Q statistic p=0.74) and no statistically significant increased risk from NAT2 acetylation (slow/rapid) for breast cancer (summary odds ratio=1.02, 95% confidence interval: 0.95, 1.08). These results suggest that there is no overall association between the NAT2 slow- or rapid-acetylation phenotype and breast cancer risk. However, some evidence suggests that smoking may modify this association.

Urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) and genetic polymorphisms in breast cancer patients

Reactive oxygen species (ROS) causes damage to DNA, but the role of ROS in breast carcinoma is still not clear. The objective of this study was to measure the urinary 8-OHdG levels of breast cancer patients at each stage of carcinogenesis and assess its association with the development of breast cancer. Sixty patients with malignant breast tumors were matched with 60 control subjects of the same ages in this case control study. Urinary 8-OHdG levels were significantly higher among breast cancer patients than among the control subjects, after making adjustments for confounders such as smoking, coffee consumption and use of oral contraceptives. The breast cancer patients were divided into three groups based on the stages of their cancer; urinary 8-OHdG levels decreased with each stage of breast carcinoma. Using multiple regression and logistic models adjusted for other covariates, urinary 8-OHdG levels significantly correlated with the development of breast cancer. However, it was found that breast cancer was not significantly influenced by CYP1A1, CYP1M1 or NAT2 polymorphisms. In conclusion, it was found that oxygen radical generation occurred within carcinoma cells, but the role of polymorphism of specific genes in the development of breast cancer should be evaluated.

Is the association between cigarette smoking and breast cancer modified by genotype? A review of epidemiologic studies and meta-analysis

Epidemiologic studies have examined the association between cigarette smoking and breast cancer risk according to genotype with increasing frequency, commensurate with the growing awareness of the roles genes play in detoxifying or activating chemicals found in cigarette smoke and in preventing or repairing the damage caused by those compounds. To date, approximately 50 epidemiologic studies have examined the association between smoking and breast cancer risk according to variation in genes related to carcinogen metabolism, modulation of oxidative damage, and DNA repair. Some of the findings presented here suggest possible effect modification by genotype. In particular, 14 epidemiologic studies have tended to show positive associations with long-term smoking among NAT2 slow acetylators, especially among postmenopausal women. Summary analyses produced overall meta-relative risk (RR) estimates for smoking of 1.2 [95% confidence interval (95% CI), 1.0-1.5] for rapid acetylators and 1.5 (95% CI, 1.2-1.8) for slow acetylators. After stratification by menopausal status, the meta-RR for postmenopausal slow acetylators was 2.4 (95% CI, 1.7-3.3), whereas similar analyses for the other categories showed no association. In addition, summary analyses produced meta-RRs for smoking of 1.1 (95% CI, 0.8-1.4) when GSTM1 was present and 1.5 (95% CI, 1.1-2.1) when the gene was deleted. Overall, however, interpretation of the available literature is complicated by methodologic limitations, including small sample sizes, varying definitions of smoking, and difficulties involving single nucleotide polymorphism selection, which likely have contributed to the inconsistent findings. These methodologic issues should be addressed in future studies to help clarify the association between smoking and breast cancer.

Smoking and smokeless tobacco-associated human buccal cell mutations and their association with oral cancer--a review

Reported herein are the results of a structured literature review that was undertaken to (a) determine if human buccal (mouth) cell changes are associated with smoking and smokeless ("chewing") tobacco, (b) tabulate different buccal cell alterations that have been reported, (c) delineate buccal cell assays that have been used successfully, (d) determine whether buccal cell changes correlate with oral cancer as defined in clinicopathologic investigations, and (e) assess the feasibility of developing a high-throughput buccal cell assay for screening smokers for the early detection of oral cancer. The results of the studies reported herein have established that diverse buccal cell changes are associated with smoking and smokeless tobacco. This review documents also that buccal cells have been collected in a noninvasive manner, and repetitively for serial studies, from different sites of the mouth (e.g., cheek, gum, and tongue) and from normal tissue, preneoplastic lesions (leukoplakia), and malignant tumors. Tobacco-associated genetic mutations and nongenetic changes have been reported; a partial listing includes (a) micronuclei, (b) bacterial adherence, (c) genetic mutations, (d) DNA polymorphisms, (d) carcinogen-DNA adducts, and (e) chromosomal abnormalities. Clinical studies have correlated buccal cell changes with malignant tumors, and some oral oncologists have reported that the buccal cell changes are practical biomarkers. Summarily, the literature has established that buccal cells are useful not only for characterizing the molecular mechanisms underlying tobacco-associated oral cancers but also as exfoliative cells that express diverse changes that offer promise as candidate biomarkers for the early detection of oral cancer.

Dose effects in gene environment interaction: an enzyme kinetics based approach

There have been many observations of different forms of the effect of dose in toxicological and pharmacological research into gene environment interactions. In one form, the effect of genetic variation is seen to be more potent at lower doses, while in the other, the genetic variant has a stronger effect at higher doses of exposure. The application of principles of classical enzyme kinetics to this problem has led to a hypothesis that for any gain of function polymorphism, a low exposure gene (LEG) or low dose effect will always be observed, while for any loss of function polymorphism, the high exposure gene (HEG) effect will always be seen. Furthermore the dose effect is found to be independent of any effects on Vmax, but is related to effects on Km of the gene product. The hypothesis is derived from the Michaelis-Menten equation, and if supported by experimental evidence, could lead to important implications for drug dosage and toxicological risk analysis in the context of individual differences in genetic profiles.

Effect of NAT1 and NAT2 genetic polymorphisms on colorectal cancer risk associated with exposure to tobacco smoke and meat consumption

N-Acetyltransferases 1 and 2 (NAT1 and NAT2), both being highly polymorphic, are involved in the metabolism of aromatic and heterocyclic aromatic amines present in cigarette smoke and red meat cooked by high-temperature cooking techniques. We investigated the effect of differences in acetylation capacity, determined by NAT1 and NAT2 genotypes, on colorectal cancer risk associated with exposure to tobacco smoke or red meat consumption. In this population-based case-control study in Germany, 505 patients with incident colorectal cancer and 604 age- and sex-matched control individuals with genotyping data and detailed risk factor information were included. Genotyping of NAT1 and NAT2 genetic polymorphisms was done using a fluorescence-based melting curve analysis method. The association between genotypes, environmental exposures, and colorectal cancer risk was estimated using multivariate logistic regression. Colorectal cancer risk associated with active smoking was elevated after accumulation of 30(+) pack-years of smoking [odds ratio (OR), 1.4; 95% confidence interval (95% CI), 0.9-2.2] but not significantly modified by either NAT1 or NAT2 genotype. Exposure to environmental tobacco smoke was associated with an increased risk for colorectal cancer only among NAT2 fast acetylators (OR, 2.6; 95% CI, 1.1-5.9 for exposure in childhood and adulthood). Frequent consumption of red meat significantly increased colorectal cancer risk for the group comprising all NAT2 fast acetylators or carriers of the NAT1*10 allele (OR, 2.6; 95% CI, 1.1-6.1) but not among those with "slow" NAT1 and NAT2 genotypes. Our findings indicate that NAT1 and NAT2 genotypes may contribute jointly to individual susceptibility and that heterocyclic aromatic amines may play an important role in colorectal cancer associated with red meat and possibly also exposure to environmental tobacco smoke.

Cumulative genetic defects in carcinogen metabolism may increase breast cancer risk (The Netherlands)

Variants in the metabolic genes NAT1, NAT2, GSTM1 or GSTT1, may cause differences in individual detoxifying capacity of possible carcinogens. We examined the cumulative effect of putative at risk genotypes on breast cancer risk and we examined the extent to which these polymorphisms modify the association between smoking and breast cancer. A case cohort study was conducted in the DOM cohort with 676 breast cancer cases and a random sample of 669 individuals. No effect of the NAT1, NAT2 or GSTM1 genotypes on breast cancer risk was observed. However, women with GSTT1 null genotype had a 30% increased breast cancer risk compared to women with GSTT1 present (RR = 1.30 (95% confidence interval (CI) 1.04-1.64)). Smoking did not influence breast cancer risk nor did genetic variations in NAT1, NAT2 or GSTM1 in combination with smoking. Compared to women who never smoked with GSTT1 present, women with GSTT1 null genotype and who formerly smoked showed an increased breast cancer risk (RR = 2.55 (95% CI 1.10-5.90)), but current smokers who smoked 20 cigarettes or more per day did not (RR = 1.06 (95% CI 0.51-2.18)). Increasing numbers of putative at risk genotypes increased breast cancer risk in a dose dependent manner (p for trend 0.01). The risk was more than doubled in women with all four risk genotypes, RR = 2.45 (95% CI 1.24-4.86), compared to women with zero putative at risk genotypes. In conclusion, the results of this study suggest that presence of three or more putative at risk genotypes increases breast cancer risk.

NAT2 slow acetylator genotype as an important modifier of breast cancer risk

N-acetyltransferase 2 (NAT2) is a polymorphic enzyme participating in the metabolism of numerous pharmaceutical drugs and carcinogens found in tobacco smoke and diet. The NAT2 gene is highly polymorphic and several different allelic variants exist that determine the acetylator phenotype. In the course of our case-control study, we developed a new method based on fluorogenic allele-specific probes for analyzing the C282T and T341C polymorphisms of the NAT2 gene in 483 Finnish breast cancer patients and 482 healthy population controls. The slow NAT2 acetylation capacity-associated genotypes posed a somewhat increased overall breast cancer risk (odds ratio [OR], 1.32; 95% confidence interval [CI], 1.01-1.73). This association was found to be confined to the advanced (stage III or IV) breast cancer (OR, 2.60; 95% CI, 1.29-5.24). When stratified by smoking habits, women who had smoked <5 pack-years and carried a NAT2 slow acetylator genotype were at a 2.6-fold (OR, 2.55; 95% CI, 1.01-6.48) risk of breast cancer. Moreover, women with the NAT2 slow acetylator genotype and low body mass index (BMI) (<25.4 kg/m2) were at somewhat increased risk of this malignancy (OR, 1.60; 95% CI, 1.07-2.39). Our results therefore suggest that NAT2 slow acetylator genotype may be an important modifier of environmentally induced breast cancer risk in Finnish women.

A case-only analysis of the interaction between N-acetyltransferase 2 haplotypes and tobacco smoke in breast cancer etiology

Introduction

N-acetyltransferase 2 is a polymorphic enzyme in humans. Women who possess homozygous polymorphic alleles have a slower rate of metabolic activation of aryl aromatic amines, one of the constituents of tobacco smoke that has been identified as carcinogenic. We hypothesized that women with breast cancer who were slow acetylators would be at increased risk of breast cancer associated with active and passive exposure to tobacco smoke.

Methods

We used a case-only study design to evaluate departure from multiplicativity between acetylation status and smoking status. We extracted DNA from buccal cell samples collected from 502 women with incident primary breast cancer and assigned acetylation status by genotyping ten single-nucleotide polymorphisms. Information on tobacco use and breast cancer risk factors was obtained by structured interviews.

Results

We observed no substantial departure from multiplicativity between acetylation status and history of ever having been an active smoking (adjusted odds ratio estimate of departure from multiplicativity = 0.9, 95% confidence interval 0.5 to 1.7) or ever having had passive residential exposure to tobacco smoke (adjusted odds ratio = 0.7, 95% confidence interval 0.4 to 1.5). The estimates for departure from multiplicativity between acetylation status and various measures of intensity, duration, and timing of active and passive tobacco exposure lacked consistency and were generally not supportive of the idea of a gene–environment interaction.

Conclusion

In this, the largest case-only study to evaluate the interaction between acetylation status and active or passive exposure to tobacco smoke, we found little evidence to support the idea of a departure from multiplicativity.

NAT2 fast acetylator genotype is associated with an increased risk of lung cancer among never-smoking women in Taiwan

The correlation between cooking oil fumes, containing relatively higher amounts of heterocyclic amines, and female lung cancer has been revealed. The association of genetic polymorphisms of CYP1A2 and NAT2, two major enzymes responsible for the metabolism of heterocyclic amines, with lung cancer has been investigated with inconclusive results. In this study targeted on never-smoking population with 162 lung cancer patients and 208 non-cancer controls, while the distributions of CYP1A2 phenotypes in lung cancer patients were comparable to that in controls, NAT2 fast acetylators had an OR of 2.44 (95% CI 1.40-4.23, P=0.002) and 2.56 (95% CI 1.37-4.80, P=0.003) for lung cancer in overall and female cases, respectively, but not in males. These results suggested never-smoking females with NAT2 fast acetylator were more prone to lung cancer and reflected the possibility that exposure to heterocyclic amines may contribute to the female lung cancer development in Taiwan.

N-acetyltransferase 2 (NAT2) genotypes, cigarette smoking, and the risk of breast cancer

N-acetyltransferases (NATs) are important catalytic enzymes that metabolize carcinogenic arylamines. NAT2 genotype might modify the role of cigarette smoking, a source of arylamine exposure, in breast cancer. We conducted a nested case-control study to investigate the association between NAT2 genotype, smoking and breast cancer risk among women (110 cases, 113 matched controls) from the CLUE II cohort in Washington County, MD. Compared to women with the slow acetylator genotype, the main effects odds ratios (OR) for NAT2 were 1.4 for the intermediate acetylator genotype (95% confidence limits (CL) 0.7, 2.7) and 3.6 for the homozygous rapid acetylator genotype (95% CL 1.1, 11.4) (P for trend = 0.05). Smoking was associated in the direction of increased breast cancer risk in slow acetylators (e.g., >15 pack-years versus never smokers OR 2.0; 95% CL 0.7, 5.8) but not in rapid acetylators. These associations were not statistically significant in the total study population, but a statistically significant interaction between smoking and NAT2 acetylator status was present in postmenopausal women. The main effect of NAT2 in the direction of increased risk suggests that exposures to NAT2-activated carcinogens other than cigarette smoke may be important in this study population. The results for smoking were consistent with an inactivation role for NAT2 in breast cancer.

N-acetyltransferase (NAT2) polymorphism and breast cancer susceptibility: a lack of association in a case-control study of Turkish population

Increased exposure to environmental carcinogens, including several aromatic and heterocyclic amines (HAs), is suspected to be one factor contributing to incidence of breast cancer. The N-acetyltransferase 2 (NAT2) acetylation polymorphism have been associated with a number of drug-induced toxicities and cancer in various tissues, resulting from decreased capacity to activate/deactivate several aromatic amine, hydrazine drugs, as well as HA carcinogens. Ethnic differences exist in NAT2 genotype frequencies, which maybe a factor in cancer incidence. Our present case-control study in Turkey was performed to explore the association between NAT2 genetic polymorphism and individual susceptibility to breast cancer. The NAT2 genotypes (*4, *12A, *5A, *5B, *5C, *6, *7) were determined using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in 84 breast cancer patients and 103 healthy controls, and 50% and 56.3%, respectively, were found to be slow acetylator genotypes. There was no significant difference in risk for breast cancer development among patients with rapid and slow acetylators, with adjusted odds ratio 0.78 (95% confidence interval 0.44 to 1.38). Also, risk was not affected by different variables. To our knowledge, this is the first genetic study on the association of NAT2 genotypes with breast cancer in the TUrkish population, and this finding showed that NAT2 polymorphism does not play an important role in breast cancer risk of Turkish women by altering the capacity in deactivation of environmental carcinogens, even though small sample size and wide confidence interval.

Assessing Interaction in Case-Control Studies

Epidemiologic researchers often explore effect modification in case-control studies on more than one statistical scale, an approach that one expects would increase the rate of false-positive findings of interaction. For example, researchers have measured effect modification by using both a multiplicative interaction coefficient (M) in a logistic regression model and a measure of interaction on the additive scale such as the interaction coefficient from an additive relative risk regression model (A). We performed computer simulations to investigate the degree to which type I error may be inflated when statistical interactions are evaluated by using both M and A. The overall type I error rate was often greater than 5% when both tests were performed together. These results provide empiric evidence of the limited validity of a common approach to assessing etiologic effect modification. When the scale has not been specified before analysis, interaction hypothesis tests of effect modification should be interpreted particularly cautiously. Researchers are not justified in choosing the interaction test with the lowest P value.

The Effect of Environment on Breast Cancer Risk

Environmental factors are believed to explain a large proportion of breast cancer incidence. Known risk factors for breast cancer, which are related to the reproductive life of women, and other factors, such as inheritance and socioeconomic status, explain only about half of the breast cancer cases in the US. Ionizing radiation is a well established environmental risk factor for breast cancer. Chemicals that induce mammary cancer in rodents have served as leads for studies in humans, but occupational and environmental exposure to these chemicals have for the most part lacked association with breast cancer risk. However, there is recent evidence in rats that cadmium at very low doses acts as an estrogen mimic, indicating a need to investigate the effects of metals on breast cancer risk. Studies suggest that circadian rhythm disruption is linked with breast cancer, but too few studies have been done to be conclusive. Over the years, cigarette smoking as a risk factor for breast cancer has remained controversial. However, recent research has found passive smoke exposure to be associated with increased breast cancer risk, which is hypothesized to be accounted for on the basis of an antiestrogenic effect of smoking. Solar radiation has been noted to be associated with reduced breast cancer, supporting the hypothesis that vitamin D plays a protective role in reducing this risk. Although, most of the environmental factors discussed in this review have not been convincingly found to influence breast cancer risk, research suggests that environmental exposure in combination with genetic pre-disposition, age at exposure, and hormonal milieu have a cumulative effect on breast cancer risk.

Active smoking, household passive smoking, and breast cancer: evidence from the California Teachers Study

BACKGROUND

There is great interest in whether exposure to tobacco smoke, a substance containing human carcinogens, may contribute to a woman's risk of developing breast cancer. To date, literature addressing this question has been mixed, and the question has seldom been examined in large prospective study designs.

METHODS

In a 1995 baseline survey, 116 544 members of the California Teachers Study (CTS) cohort, with no previous breast cancer diagnosis and living in the state at initial contact, reported their smoking status. From entry into the cohort through 2000, 2005 study participants were newly diagnosed with invasive breast cancer. We estimated hazard ratios (HRs) for breast cancer associated with several active smoking and household passive smoking variables using Cox proportional hazards models.

RESULTS

Irrespective of whether we included passive smokers in the reference category, the incidence of breast cancer among current smokers was higher than that among never smokers (HR = 1.32, 95% confidence interval [CI] = 1.10 to 1.57 relative to all never smokers; HR = 1.25, 95% CI = 1.02 to 1.53 relative to only those never smokers who were unexposed to household passive smoking). Among active smokers, breast cancer risks were statistically significantly increased, compared with all never smokers, among women who started smoking at a younger age, who began smoking at least 5 years before their first full-term pregnancy, or who had longer duration or greater intensity of smoking. Current smoking was associated with increased breast cancer risk relative to all nonsmokers in women without a family history of breast cancer but not among women with such a family history. Breast cancer risks among never smokers reporting household passive smoking exposure were not greater than those among never smokers reporting no such exposure.

CONCLUSION

Our study provides evidence that active smoking may play a role in breast cancer etiology and suggests that further research into the connection is warranted, especially with respect to genetic susceptibilities.

N-acetyltransferase (NAT1, NAT2) and glutathione S-transferase (GSTM1, GSTT1) polymorphisms in breast cancer

To evaluate the potential association between NAT1/NAT2 polymorphisms and breast cancer, a case-control study was conducted in Korean women (254 cases, 301 controls). NAT1 *4/*10 genotype (42%) was the most common NAT1 genotype in this Korean population. The frequencies of slow, intermediate and rapid NAT2 acetylator genotype were 16, 39 and 44% in cases and 16, 42 and 42% in controls. Neither NAT1 rapid (homozygous or heterozygous NAT1 *10) (OR=1.2, 95% CI=0.8-1.9) nor NAT2 rapid acetylator genotype (OR=1.2, 95% CI=0.8-1.7) showed significant association with breast cancer risk. Although the risk of NAT2 rapid acetylator genotype in postmenopausal women (OR=1.4, 95% CI=0.7-2.8) was higher than that in premenopausal women (OR=1.1, 95% CI=0.7-1.7), those were not statistically significant. However, combinations of NAT1, GSTM1 and GSTT1 genotypes showed a significant linear gene-dosage relationship with breast cancer (p for trend=0.04) and those women with NAT2 rapid acetylator and both GSTM1 and GSTT1 null genotypes were at the elevated risk (OR=3.1, 95% CI=1.0-9.1). These results suggest that genetic polymorphisms of NAT1 and NAT2 have no independent effect on breast cancer risk, but they modulate breast cancer risk in the presence of GSTM1 and GSTT1 null genotypes.

NAT2 slow acetylation and GSTM1 null genotypes may increase postmenopausal breast cancer risk in long-term smoking women

N-acetyltransferase (NAT) 1 and 2 and glutathione S-transferase (GST) M1 and T1 are phase II enzymes that are important for activation and detoxification of carcinogenic heterocyclic and aromatic amines, as present in cigarette smoke. We studied whether genetic polymorphisms in these genes modifies the relationship between smoking and breast cancer. A nested case-control study was conducted among participants in a Dutch prospective cohort. Breast cancer cases (n=229) and controls (n=264) were frequency-matched on age, menopausal status and residence. Compared to never smoking, smoking 20 cigarettes or more per day increased breast cancer risk statistically significant only in postmenopausal women [odds ratio (OR)=2.17; 95% confidence interval (CI) 1.04-4.51]. Neither NAT1 slow genotype, or GSTT1 null genotype, alone or in combination with smoking, affected breast cancer risk. However, compared to individuals with rapid NAT2 genotype, women with the very slow acetylator genotype (NAT2*5), who smoked for 20 years showed an increased breast cancer risk (OR=2.29; 95% CI 1.06-4.95). Similarly, the presence of GSTM1 null genotype combined with high levels of cigarette smoking (OR=3.00; 95% CI 1.46-6.15) or long duration (OR=2.53; 95% CI 1.24-5.16), increased rates of breast cancer. The combined effect of GSTM1 null genotype and smoking high doses was most pronounced in postmenopausal women (OR=6.78; 95% CI 2.31-19.89). In conclusion, our results provide support for the view that women who smoke and who have a genetically determined reduced inactivation of carcinogens (GSTM1 null genotype or slow NAT2 genotype (especially very slow NAT2 genotype)) are at increased risk of breast cancer.

A null association between active or passive cigarette smoking and breast cancer risk

The effect of smoking on breast cancer risk has been null in large, well-conducted cohort studies. In a previous study, we stratified the population into active smokers, passive smokers, and never-active never-passive smokers and modeled early life cigarette smoke exposures as causal and later life cigarette smoke exposure as preventive. We observed a complex association between cigarette smoke and breast cancer risk. Using a similar design and population, this study did not confirm the earlier result. Neither ever-active smoking (adjusted odds ratio (OR) = 0.72, 95% confidence intervals (CI) 0.55-0.95) nor ever-passive smoking (adjusted OR = 0.85, 95% CI 0.63-1.1) were strongly associated with breast cancer risk compared with never-active never-passive smoking. No patterns of effects were observed in subgroup analyses.

Breast and cervical cancer screening: sociodemographic predictors among White, Black, and Hispanic women

OBJECTIVES

We evaluated the relationship between breast and cervical cancer screening and a variety of variables across race/ethnicity groups.

METHODS

Using logistic regression models, we analyzed data from the 1998 National Health Interview Survey to assess the relative importance of the independent variables in predicting use of cancer screening services.

RESULTS

Having a usual source of care was the most important predictor of cancer screening use for all race/ethnicity groups. Health insurance was associated with an increased likelihood of cancer screening. Smoking was associated with a decreased likelihood of cancer screening.

CONCLUSIONS

Regardless of race/ethnicity, most women follow mammography and cervical cancer screening guidelines. The identification of specific factors associated with adherence to cancer screening guidelines may help inform screening campaigns.

Environmental risk factors for breast cancer among African-American women

There are few unequivocably established environmental carcinogens for breast cancer in women. Nevertheless, environmental factors are believed to explain much of the international variation in breast cancer risk and possibly differences among racial/ethnic groups. Along with lifestyle, some adverse exposures may be higher in minority racial/ethnic groups and in underserved populations that experience higher ambient contamination. Associations have been found between environmental agents and breast cancer in subgroups of women who can be identified by common susceptibility traits as well as by timing of exposures at certain milestones of reproductive life. Susceptibility can be defined by social, environmental, and genetic modalities-factors that may predominate in certain racial/ethnic groups but that also transcend racial/ethnic boundaries. For example, genes involved in transcription and estrogen metabolism have rapid variants that are more prevalent among African-Americans, yet risk accompanying metabolic changes from these genes will prevail in all racial/ethnic groups. Lack of reliable exposure assessment remains a principal obstacle to elucidating the role of environmental exposures in breast cancer. Resources must be identified and consolidated that will enable scientists to improve exposure assessment and to assemble studies of sufficient size to address questions regarding exposure, susceptibility, and vulnerability factors in breast cancer. Breast cancer studies should be expanded to examine combinations of chemicals as well as competing or complementary exposures such as endogenous hormones, dietary intake, and behavioral factors.

Differences between children and adults: implications for risk assessment at California EPA

The California legislature enacted a law requiring the California Environmental Protection Agency (Cal/EPA) Office of Environmental Health Hazard Assessment (OEHHA) to evaluate whether our risk assessment methodologies are adequately protective of infants and children. In addition both OEHHA and the California Air Resources Board must examine whether the Ambient Air Quality Standards set for criteria air pollutants and the health values developed for air toxics are adequately protective of infants and children. We have initiated a program to look at potential differences in response to toxicants between children and adults. We are evaluating this issue from the perspective of exposure differences as well as toxicokinetic and toxicodynamic differences between children and adults. Data on specific chemicals are rather limited. As a result, we will be pooling information to determine whether there are generic differences between children and adults that may be applicable to risk assessment in general or to risk assessment of specific classes of compounds. This paper discusses the rationale for approaching the issue of determining whether our risk assessment methods are adequate for infants and children and includes a discussion of some of the available information on both qualitative and quantitative differences in response to toxicants between children and adults or immature and mature laboratory animals. We provide examples of differences between children and adults in absorption, metabolism, and excretion of toxicants as well as qualitative differences in toxic response.

Cigarette smoking and breast cancer risk: a long latency period?

The association between cigarette smoking and breast cancer risk remains unclear. Few studies have examined cigarette smoking of very long duration as there may not have been a sufficient number of long-term smokers in studies conducted before the 1980s. Therefore, we examined the association between smoking and breast cancer risk using data from participants in a randomized controlled trial of screening for breast cancer involving 89,835 women aged 40-59 years at recruitment and with up to 40 years of smoking duration at that time. Women with breast cancer diagnosed through 31 December 1993 were identified by linkage to the Canadian Cancer Database. Cox proportional hazards models were used to estimate rate ratios (RRs) and 95% confidence intervals (CIs). During an average of 10.6 years of follow-up, we observed 2,552 incident cases of breast cancer. We found a positive association between cigarette smoking and breast cancer risk, driven mainly by women who had smoked for several decades and who, therefore, had commenced smoking many years earlier. Relative to never-smokers, women who had smoked 40 years or more and 20 cigarettes/day or more were at the highest risk (RR = 1.83, 95% CI 1.29-2.61); for women who had commenced smoking 40 years or more before assessment (a measure of smoking latency rather than duration and intensity), the RR was 1.22 (95% CI 0.99-1.59). Our findings suggest that smoking of very long duration and high intensity may be associated with increased risk of breast cancer.

GSTT1 null genotype increases risk of premenopausal breast cancer

The NAT2, GSTM1 and GSTT1 genes are known candidate cancer susceptibility markers and have been investigated in breast cancer susceptibility with conflicting results. We conducted a case-control study to investigate the role of NAT2, GSTM1 and GSTT1 in premenopausal breast cancer. Women with the GSTT1 null genotype were found to have a significant 3.15-fold increased risk of breast cancer (95% CI = 1.7-5.8), while GSTM1 and NAT2 genotypes were not associated with breast cancer risk. Our results suggest that the GSTT1 null genotype may play a role in early onset breast cancer.