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Breast cancer, alcohol, and tobacco

Study
Results
Comment

One of the most important developments in recent years has been collaboration between research groups to pool information on individual patients better to understand disease development and treatment. One such is investigating breast cancer [1].

Study

The influence of alcohol and tobacco on breast cancer was examined in 65 studies contributing individual patient data on over 66,000 women with breast cancer and nearly 130,000 controls. Of these, 53 had information on both alcohol and tobacco in 58,500 cases of breast cancer and 95,000 controls.

Case-control and cohort studies were eligible if they recruited at least 100 women with invasive breast cancer and recorded information on reproductive factors and use of hormonal therapies. Information on individual women was collated and analysed centrally to use as similar definitions as possible. One drink was 12 grams of alcohol in the USA and Italy, 8 grams in the UK and 10 grams elsewhere.

Results

The average age at diagnosis of breast cancer was 52 years. Women with higher alcohol consumption also tended to smoke more in cases and controls. Only 37% of women who never drank alcohol had ever smoked, a proportion rising to about 70% in those with the highest alcohol intake.

In women who had never drunk alcohol (22,000 cases and 41,000 controls) there was no relationship between breast cancer and smoking history (relative risk 1.03). Because of the relationship between increased alcohol consumption and increased smoking, no reliable information could be drawn for smokers who also drank alcohol.

The relative risk of breast cancer was positively linked to increased daily alcohol consumption (Figure 1), to the same extent in women who had never smoked and in those who had ever smoked. Overall, the increase in the relative risk of breast cancer rose by 7% for each 10 grams per day of alcohol intake. There was no significant variation in the trend for any of 15 factors (race, education, BMI, breastfeeding etc).

Figure 1: Relationship between daily alcohol consumption and relative risk for breast cancer in women



The cumulative incidence of breast cancer up to the age of 80 years is between eight and 10 per 100 in women in developed countries. The average consumption of alcohol was 6 grams per day, which would mean that about 4% of breast cancers in developed countries could be attributed to alcohol. The cumulative incidence of breast cancer by 80 years of age for women consuming different levels of daily alcohol a day is shown in Figure 2.

Figure 2: Cumulative incidence of breast cancer by age 80 and number of drinks per day



Comment

This is fantastic stuff, which can be relied upon because of the mass of information and the quality of the analysis. It firmly makes alcohol an issue for women. It means that benefits of alcohol for the heart have to be balanced against some increased risk of breast cancer.

But at moderate amounts of alcohol, one or two drinks a day, the increase in risk is moderate.

Reference:

  1. Collaborative group on hormonal factors in breast cancer. Alcohol, tobacco and breast cancer - collaborative reanalysis of individual data from 53 epidemiological studies, including 58 515 women with breast cancer and 95 067 women without the disease. British Journal of Cancer 2002 87: 1234-01245.
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