Alcohol and Breast Cancer

Interview with Dr. William Waddell

A recent study reporting that alcohol was related to the incidence of breast cancer created strong public interest in its conclusions. This interview by Prof. David Hanson explores the study and its findings with Dr. William Waddell, who is Professor and Emeritus Chair of the Department of Pharmacology and Toxicology at the University of Louisville.

Dr. Hanson--

Dr. Waddell, the recent study of breast cancer 1 has been described as "definitive." I understand that you disagree with that characterization.

Dr. Waddell--

Yes, I do. The study was certainly not "definitive" and should not be conveyed to the public that way. There are numerous uncertainties, biases, and matters of judgment that prevent this study from being any more conclusive than any of those that precede it. The question is still far from settled and the present study could just as well be interpreted, after carefully considering all the issues, as evidence that drinking alcohol has nothing to do with breast cancer.

Dr. Hanson--

Why is that?

Dr. Waddell--

The authors identified seven studies that met their requirements for analysis 2. However, they chose to exclude the Adventist Health Study 3 and only analyzed six. Importantly, the excluded study found the best predictor of the incidence of breast cancer to be education. That is, the higher the education, the higher the occurrence of breast cancer. But remember, they discarded this study.

Dr. Hanson--

So what did they find in the remaining six studies?

Dr. Waddell--

They found that there was no significant increase in breast cancer in any of the four consumption categories below 30 grams per day or in the category of over 60 grams per day. It was only in the category between 30 and 60 grams per day that a significant increase in breast cancer was seen. In other words, in only one out of six consumption categories was there a significant increase in breast cancer.

Dr. Hanson--

Only one out of six? That doesn't seem "definitive."

Dr. Waddell--

It isn't. Furthermore, it's important to stress that the highest level of alcohol consumption did not show a significant increase in cancer. There is not another carcinogen (cancer causing substance) of which I am aware, in either in human or animal reports, that does not show a clear pattern in which the highest consumption level shows the greatest number of tumors.

Dr. Hanson--

The authors only looked at six studies. Have there been many other studies of alcohol and breast cancer?

Dr. Waddell--

Yes, there have been a great many studies on this important matter. 4 Although many have found an increase in the incidence of breast cancer with alcohol consumption, there are some that not only fail to find an increase but actually show a statistically significant decrease. Even among those showing a positive association (that is, more cancer goes with more drinking), many are not statistically significant and none shows a strong relationship between drinking and cancer.

Dr. Hanson--

You say "statistically significant." Would you explain what that means?

Dr. Waddell--

Of course. It means that the results are greater than what statisticians would expect to have occured by mere chance.

Dr. Hanson--

Wasn't there a significant relationship between breast cancer and alcohol consumption in one of the six consumption categories?

Dr. Waddell--

Yes, but it was only one out of the six, and very importantly, it wasn't at the highest level of consumption. Furthermore, as Sir Austin Bradford Hill has pointed out, determining statistical significance is merely the first step in studying possible associations for possible causation. There is no substitute for the judgment that is required beyond this first step. This is especially true for alcohol and breast cancer because so many studies have been done without showing consistent results and because so many other factors have been identified as possible causes of breast cancer (for example, fat intake, body size, education, menstrual status, family history, breast cancer genes, etc.). Among the most important points identified by Hill are strength of the association , consistency of the association, and "dose response" (in this case, the more alcohol consumed, the more often cancer should be found).The studies on alcohol and breast cancer fail to satisfy any of these important points.

Dr. Hanson--

Thank you, Dr. Waddell. Do you have any other thoughts?

Dr. Waddell--

Yes. The question of cancer caused by substances that we consume is an important one and must be answered by careful research and good evidence. This widely reported study provides no good evidence and basis for action to reduce cancer. However, it has needlessly alarmed many people. How quickly we forget the premature and unfounded furor over saccharin and bladder cancer, coffee and pancreatic cancer, and many others that were prematurely and falsely implicated as problems.

 

Dr. William Waddell received his M.D. from the University of North Carolina at Chapel Hill. As a toxicologist, his research has focused on the metabolism of drugs, on the specific mechanisms by which substances cause cancer, and on cancer caused by chemicals. His expertise is widely sought by both his scientific peers and by various organizations concerned with such issues.

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