Alcohol and tobacco consumption are closely correlated and published results on their association with breast cancer have not always allowed adequately for confounding between these exposures. Over 80% of the relevant information worldwide on alcohol and tobacco consumption and breast cancer were collated, checked and analysed centrally. Analyses included 58 515 women with invasive breast cancer and 95 067 controls from 53 studies. Relative risks of breast cancer were estimated, after stratifying by study, age, parity and, where appropriate, women's age when their first child was born and consumption of alcohol and tobacco. The average consumption of alcohol reported by controls from developed countries was 6.0 g per day, i.e. about half a unit/drink of alcohol per day, and was greater in ever-smokers than never-smokers, (8.4 g per day and 5.0 g per day, respectively). Compared with women who reported drinking no alcohol, the relative risk of breast cancer was 1.32 (1.19 -1.45, P50.00001) for an intake of 35 -44 g per day alcohol, and 1.46 (1.33 -1.61, P50.00001) for 545 g per day alcohol. The relative risk of breast cancer increased by 7.1% (95% CI 5.5 -8.7%; P50.00001) for each additional 10 g per day intake of alcohol, i.e. for each extra unit or drink of alcohol consumed on a daily basis. This increase was the same in ever-smokers and never-smokers (7.1% per 10 g per day, P50.00001, in each group). By contrast, the relationship between smoking and breast cancer was substantially confounded by the effect of alcohol. When analyses were restricted to 22 255 women with breast cancer and 40 832 controls who reported drinking no alcohol, smoking was not associated with breast cancer (compared to never-smokers, relative risk for ever-smokers=1.03, 95% CI 0.98 -1.07, and for current smokers=0.99, 0.92 -1.05). The results for alcohol and for tobacco did not vary substantially across studies, study designs, or according to 15 personal characteristics of the women; nor were the findings materially confounded by any of these factors. If the observed relationship for alcohol is causal, these results suggest that about 4% of the breast cancers in developed countries are attributable to alcohol. In developing countries, where alcohol consumption among controls averaged only 0.4 g per day, alcohol would have a negligible effect on the incidence of breast cancer. In conclusion, smoking has little or no independent effect on the risk of developing breast cancer; the effect of alcohol on breast cancer needs to be interpreted in the context of its beneficial effects, in moderation, on cardiovascular disease and its harmful effects on cirrhosis and cancers of the mouth, larynx, oesophagus and liver. Many epidemiological studies have investigated the relationship between breast cancer and the consumption of alcohol and/or tobacco. References to over 80 studies that have collected relevant data, as well as to reviews of the subject, are given in Appendix II (www. bjcancer.com). The published results from these studies have general...
SummaryThe results of the Swedish two-county study are analysed with respect to tumour size, nodal status and malignancy grade, and the relationship of these prognostic factors to screening and to survival. It is shown that these factors can account for much of the differences in survival between incidence screen detected, interval and control group cancers but to a lesser extent for cancers detected at the prevalence screen where length bias is greatest. Furthermore, examination of the relationships among the prognostic factors and mode of detection indicates that malignancy grade, as a measure of inherent malignant capacity, evolves as a tumour grows. The proportion of cancers with poor malignancy grade is several fold lower for cancers of diameter less than 15 cm than for cancers greater than 30 cm, independent of the length bias of screening. The implications of these findings for screening frequency are briefly discussed.It has been shown that mortality from breast cancer can be reduced by mass screening using mammography (Shapiro et al., 1982;Tabar et al., 1985), a reduction resulting from earlier diagnosis. The natural history of breast cancer, however, is clearly heterogeneous, with substantial variation among tumours in their malignant potential, rate of growth and prognosis. Further, little is known of the rate at which prognosis deteriorates as a tumour develops or conversely how prognosis improves as the time of diagnosis is advanced.It is known that screening does reduce rates of larger tumours and of metastases Tabar et al., 1987). Moreover, these factors affect survival, as does malignancy grades. However, these relationships have not been fully quantified in a screening context, so the mechanism whereby screening can reduce mortality is not fully understood. The purpose of the present paper is to examine, using the results of the Swedish two-county study:(1) the relationships among the prognostic factors: tumour size, nodal involvement and malignancy grade; (2) the change in these factors brought about by screening; (3) the extent to which the change in the distributions of prognostic factors achieved by screening can account for the mortality reduction; (4) (Bloom & Richardson, 1957;Scarff & Torloni, 1968) was determined by one pathologist in each county, but as results demonstrate, there were differences between the two counties in proportions of grades 1, 2 and 3, probably reflecting subjectivity in classification of tumour grade rather than a difference in the two tumour populations. No such differences were observed between counties for tumour size or node status.Statistical analysis of associations among tumour characteristics was performed using log-linear modelling and logistic regression (Aitkin et al., 1989). These methods yield likelihood ratio (deviance) chi-squared tests for significance of associations and odds ratio estimates of relative risks (for example of being nodes positive for given grade relative to grade 1). Survival analysis was performed using proportional hazards regres...
Breast cancer cases diagnosed in women aged 50 -69 since 1990 to 1996 in the City of Florence were partitioned into those who had been invited to screening prior to diagnosis and those who had not. All cases were followed up for vital status until 31 December 1999. The cumulative number of breast cancer deaths among the cases were divided by screening and invitation status, to give the rates of cancers proving fatal within a period of 8 years of observation (incidence-based mortality). We used the incidence-based mortality rates for two periods (1985 -86, 1990 -96), pre and during screening. The incidencebased mortality ratio comparing 1990 -96 and 1985 -86 was 0.50 (95% CI : 0.38 -0.66), a significant 50% reduction. For noninvited women, compared to 1985-86, there was a 41% significant mortality reduction (RR=0.59, 95% CI : 0.42 -0.82). The comparable reduction in those invited was a significant 55% (RR=0.45, 95% CI : 0.32 -0.61). The incidence ratio of rates of cancers stage II or worse was close to one when the noninvited in 1990 -96 were compared with 1985 -86 (RR=0.97, 95% CI : 0.78 -1.21). Excluding prevalent cases, the rate of stage II+ breast cancer cases was 42% lower in Screened women compared with the noninvited (RR=0.58, 95% CI : 0.45 -0.74). This study confirmed that new treatments and the first rounds of the screening programme contributed to reducing mortality from breast cancer.
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