Alcoholic beverages and breast cancer: some observations on published case-control studies

Meta-analysis of Studies of Alcohol and Breast Cancer with Consideration of the Methodological Issues

OBJECTIVE

To give an up-to-date assessment of the association of alcohol with female breast cancer, addressing methodological issues and shortfalls in previous overviews.

METHODS

Meta-analysis of studies (any language) providing original data on incidence of first primary breast cancer and alcohol. Two reviewers independently extracted data. Study quality assessed by objective criteria including degree of control for confounding; funnel plots examined for publication bias; meta-regression techniques to explore heterogeneity. Risks associated with drinking versus not drinking and dose-response not constrained through the origin estimated using random effects methods.

RESULTS

Ninety-eight unique studies were included, involving 75,728 and 60,653 cases in drinker versus non-drinker and dose-response analyses, respectively. Findings were robust to study design and analytic approaches in the meta-analyses. For studies judged high quality, controlled for appropriate confounders, excess risk associated with alcohol drinking was 22% (95% CI: 9-37%); each additional 10 g ethanol/day was associated with risk higher by 10% (95% CI: 5-15%). There was no evidence of publication bias. Risk did not differ significantly by beverage type or menopausal status. Estimated population attributable risks were 1.6 and 6.0% in USA and UK, respectively.

CONCLUSIONS

Taking account of shortcomings in the study base and methodological concerns, we confirm the alcohol-breast cancer association. We compared our results to those of an individual patient data analysis, with similar findings. We conclude that the association between alcohol and breast cancer may be causal.

Derivation of tolerable upper alcohol intake levels in Germany: a systematic review of risks and benefits of moderate alcohol consumption

BACKGROUND

The objective of this study is to weigh the risks of moderate alcohol consumption against its benefits and, as a result, to derive tolerable upper alcohol intake levels (TUALs) for the German adult population.

METHODS

Human studies assessing the effects of moderate alcohol consumption (< or = 40 g/day) on coronary heart disease, stroke, blood pressure, diseases of the liver, gallbladder, bile duct, and pancreas, cancer of the mouth/pharynx/larynx/oesophagus, stomach, colon/rectum, and breast, foetal alcohol syndrome/foetal alcohol effects, as well as all-cause mortality, published in the 10-15 years before 1999, have been systematically reviewed. The quality of studies has been evaluated using a self-constructed evaluation scheme. As a result of comparing the critical endpoints of alcohol intake related to morbidity and mortality, the TUALs have been derived.

RESULTS

The TUALs have been set at 10-12 g/day for healthy women and 20-24 g/day for healthy men of the adult population (18 years and older). Additional guidelines on alcohol use have been defined, taking into account further important aspects like alcohol consumption patterns and high-risk groups.

CONCLUSIONS

The TUALs are not intended to be recommended intake levels. However, if the TUALs and the additional guidelines are followed, a relation of alcohol consumption to an increased risk of alcohol-associated diseases is unlikely for the majority of the population.

Screening mammography: a missed opportunity

By age 80, 1/10 women will be diagnosed with breast cancer. Both positive and negative associations have been reported between alcohol consumption and breast cancer. Minority women are less likely to undergo breast cancer screening. All women admitted for alcohol detoxification in an urban setting with a high minority population were offered screening mammography, using American Cancer guidelines. Women with previously diagnosed breast cancer were excluded from the study. The mammograms were performed by standard technique in the hospital radiology department. The subjects with positive mammograms were referred for further diagnostic studies, as determined by the internist managing the patient's care. Of the 117 women admitted, 28 were excluded due to age. Only one woman, previously treated for breast cancer, was also excluded. Of the 88 women screened, abnormalities were detected in 32. The women with normal mammograms did not differ from those with abnormal studies in: (1) age; (2) years of alcohol consumption; (3) age at menarche; (4) parity; (5) age at first full term pregnancy; and (6) personal history of benign breast disease or family history of breast cancer. The alcohol detoxification unit provides a unique opportunity to screen women for breast cancer. Compliance with initial screening is high but resistance is encountered if further diagnostic studies are required to evaluate suspicious lesions. Surprisingly, in this study, the number of suspicious lesions detected was not higher than expected.

Assessing moderate alcohol consumption as a personal risk factor

Alcohol consumption has been associated with favorable as well as adverse health effects. Risk factors represent formal predictors that such outcomes will occur more frequently than due to chance alone, but these epidemiological indicators are only average statistical associations, and by themselves do not prove causality. However, the concept of risk factors assumes that the total health hazard for any defined age-sex-race cohort can be segmented into one component accounted for by the effects of specified risks and one component accounted for by the "basic average health hazard". Typically, the risk-outcome relationships of drinking are not linear. A so-called U-shaped association between drinking and total mortality has been proposed, whereby moderate drinkers have lower mortality than either abstainers or heavy drinkers. When the relative risk of drinking is formulated as a quotient (odds ratio) with the basic health hazard used as the denominator, appropriate definition and selection of the reference population used to derive the latter becomes pivotal. Equally crucial is the choice of the yardstick for outcome. To date such objective measures as morbidity or mortality have been used almost exclusively, but the complex impact of drinking would demand assessment of physical, mental and social functioning. Finally, the threshold value above which drinking should be considered epidemiologically significant is a judgmental issue, where ethical bias can express itself. By their very nature epidemiological risk estimates are inadequate if not inapplicable to advise everyone that moderate drinking is a personal medical benefit or risk. To render any health factor identified by statistical relationships applicable in individual medical counselling demands validation by clinical trial of its sensitivity, specificity, predictive values, and associated benefits as well as costs. This information has not been compiled, but nevertheless, epidemiological correlations can be used to compare risks and benefits among different health factors to arrive at informed personal choices.

Cigarette smoking and breast cancer

OBJECTIVE

To investigate cigarette smoking in relation to the risk of breast cancer.

DESIGN

Interviews with women referred for mammography.

SETTING

Hjørring District Hospital, a public, population based hospital in Denmark.

SUBJECTS

3240 women aged 15-92 years referred for mammography during 1 June 1989 to 1 November 1991.

MAIN OUTCOME MEASURES

Smoking, parity, age, reason for referral, breast cancer.

RESULTS

In a multiple logistic regression analysis adjusted for six variables a pronounced increased risk of breast cancer was found in women who had smoked for over 20 years, and this was significant in women who had smoked for over 30 years (odds ratio 1.6, 95% confidence interval 1.1 to 2.3). The median age of women with breast cancer was 59 (range 31-81) years for smokers and 67 (38-92) years for nonsmokers. The difference of eight years between the median ages was significant (P < 0.01).

CONCLUSION

Smoking may increase the risk of breast cancer after 30 years of smoking.

Diet and breast cancer: trial and error?

The risk of developing breast cancer in females is determined by characteristics of hormone- and pregnancy-related tissue growth and development and mechanistic interactions between carcinogens and molecular targets and clonal selection of cell lines. Animal models have substantiated the idea that breast tissue may have periods of increased sensitivity to carcinogens and that dietary fat, and particularly energy intake, affect cancer risk. In epidemiological research, ecological studies clearly demonstrated positive associations between dietary fat and breast cancer risk, but individual-based case-control studies and cohort studies did not support a causal interpretation. The debate is now whether the ecological fallacy or biases in analytical epidemiology account for the apparent discrepancy, and the character of the debate is mainly of a methodological nature. Ecological and analytical studies, however, are fundamentally different with respect to the time- and age-axes considered. The lack of association in analytical studies addressing late-stage carcinogenesis may be attributed to exposures being relevant earlier in life. Analytical studies that integrate insights relating to periods of increased tissue susceptibility and mechanistic models of carcinogenic action may be fruitful in producing new outlooks for breast cancer prevention.