The latest critique from The ISFAR considers research into the association of alcohol consumption with breast cancer

The latest critique from The ISFAR considers research into the association of alcohol consumption with breast cancer

The study concerned is based on a large number of women participating in a clinical trial (enhanced screening for certain cancers versus routine care) focusing on prostate, lung, colorectal, and ovarian cancer.

During a follow-up period averaging about nine years, a total of 1,905 women were diagnosed with invasive breast cancer. The analyses showed that an increase in cancer risk was associated with alcohol intake for estrogen and progestin positive (ER+/PR+) tumours, but not for other histologic types of breast cancer.

The increased risk was predominantly seen among PR+ cancers, as there was no evidence of an increase in risk from alcohol for women with ER+/PR- tumours. An association with the highest category of alcohol intake was noted for ductal (the most prominent type), lobular, and mixed ductal/lobular tumours, but a clear dose-response curve was not present. The study's authors conclude that alcohol consumption is associated with some, but not all breast cancer subtypes, and that future research should include precise definition of subtypes of cancer.

Forum reviewers considered this to be a well-done analysis.

There were some questions about the characteristics of the participants in the study that could affect generalisability of the results. For example, the cohort of women in this study were more highly-educated, more likely to have a positive family history of breast cancer, to be smokers, and perhaps more obese that the general population.

Of more concern, however, was the lack of ability to evaluate a number of other potential risk factors for breast cancer: folate levels and other dietary factors, the pattern of drinking (regular versus binge), potential changes in drinking after the baseline measurement, type of beverage, or the HER2 status of tumours.

The paper's finding of an increase in breast cancer risk, in comparison with non-drinkers, even for women reporting less than ½ drink per week (RR 1.15, CI 0.97, 1.39) and 0.5 - < 1 drink per week (RR 1.25, CI 1.03, 1.53), suggests that residual confounding must also be considered; it is unlikely that such small amounts of alcohol would have a physiological effect. 

Overall, the present study shows a significant increase in the risk of among women in a cancer prevention trial who, at baseline, indicated that they were consuming even less than 1 drink per week. The increase was exclusively in ER+/PR+ tumours, but not in ER+/PR- or ER-/PR- tumours. 

In future research on this association, information on folate levels and drinking pattern, especially on type of beverage consumed and on evidence of under-reporting of alcohol intake, will be important in better defining how alcohol consumption relates to the risk of breast cancer.

While the results of this study are important in studying the etiology of breast cancer (as alcohol appears to relate only to hormone receptor positive tumours), the findings may not necessarily help individual women know how their alcohol consumption by itself may relate to their overall risk of the disease.

To read the full critique, click here.

These critiques are published with the permission of The ISFAR.