Experts struggle with clinical implications of alcohol and link to breast cancer risk

About 20,000 extra cancers will be diagnosed annually in the U.S. due to alcohol drinking, researchers say. What role oncologists should play in counseling their patients remains unclear.

Information on the relative health benefits and risks of alcohol consumption seems to come out on a monthly basis, but the early days of 2009 were particularly flooded with such reports. Three high-profile studies offered more evidence of a significant association between alcohol consumption and breast cancer risk.

In the absence of a randomized controlled trial, which is extremely unlikely, experts agree the preponderance of existing data provides as concrete an indictment as can be expected. But the clinical implications of the link between alcohol and breast cancer are less clear.

Researchers have yet to agree on a threshold level of alcohol consumption above which the increased risk of breast cancer becomes clinically significant, making it difficult for clinicians to give patients specific recommendations.

Studies also have yet to explore the extent to which the breast cancer risk associated with alcohol might outweigh any potential benefits of light to moderate drinking, particularly those related to cardiovascular health.

The picture is even more complicated for clinical oncologists. Though their role in cancer prevention is increasing, oncologists often do not see patients until a diagnosis has already been made, so that opportunities for intervention are more likely to include counseling of cancer survivors and education of primary care physicians.

In a February policy statement encouraging oncologists to provide prevention and risk assessment services, ASCO acknowledged that obtaining reimbursement for such services is likely to be a challenge. Still, with the recent studies on alcohol and breast cancer making headlines in the consumer media, it’s a topic that clinicians should be prepared to discuss with their patients, according to experts who spoke with Oncology News International.

Threshold estimates
“Of course, oncologists are going to be advising their patients about what to do, but they also might be advising the sisters and daughters who don’t have breast cancer but might be at risk. If a woman already has breast cancer or is at very high risk and is interested in reducing that risk, I would think the advice should be very moderate about drinking,” said Arthur L. Klatsky, MD, an adjunct investigator in the division of research at Kaiser Permanente Medical Center in Oakland, Calif., and senior author of one of the recent studies (Eur J Cancer 455:843-850, 2009).

Dr. Klatsky and colleagues analyzed the baseline alcohol consumption patterns of more than 70,000 women, 2,829 of whom went on to develop breast cancer during a mean follow-up period of 16 years. Compared with lifelong abstainers, those who reported consuming less than one drink per day showed a relative risk of developing breast cancer of 1.08, 1.21 for one to two drinks per day, and 1.38 for three or more drinks per day. The relative risk for less than one drink per day was not statistically significant, suggesting that the threshold of significance lies somewhere between one and two drinks per day.

“A lot of studies show fairly convincingly that heavier drinking is related to a higher risk of breast cancer,” Dr. Klatsky said. “While it’s important to know that, it doesn’t make a whole lot of difference in terms of advising patients about healthy lifestyles because it’s clearly undesirable to be a heavy drinker for a lot of reasons.”

“Most people who drink are not heavy drinkers; they’re light to moderate drinkers,” he added. “Studies have been a little more conflicting about lighter drinking. But I honestly don’t think a few drinks a week will increase the risk significantly.”

Million Women Study
The much-publicized Million Women Study took a different approach to assessing the effect of alcohol consumption on the risk of developing cancer in any of 21 common anatomical sites. Rather than following the categorical modeling utilized in the Kaiser study, University of Oxford researchers calculated the log-linear trends in increased risk per drink per day in more than 1.28 million women who were followed for an average of 7.2 years.

For breast cancer, the researchers estimated a statistically significant 12% increase in risk for every 10 g drink consumed per day, compared with nondrinkers.

Although the trends for some other site-specific cancers indicated higher risk levels (eg, 24% increase per drink per day for liver cancer, 44% for larynx), the increase associated with breast cancer is a greater public health concern, according to Naomi E. Allen, PhD, an investigator in the Cancer Epidemiology Unit at Oxford and lead author of the study (J Natl Cancer Inst 101:296-305, 2009).

“This study shows that even relatively low levels of drinking increase a woman’s risk of developing cancer,” Dr. Allen explained. “Although the risk of breast cancer associated with drinking an extra drink each day is less than that of some other cancers, most of the excess risk of moderate alcohol drinking is due to breast cancer because it is so common.”

“About 30,000 extra cancers will be diagnosed each year in the U.S. due to alcohol drinking, and of those, about 20,000 will be breast cancer,” she added.

Not better in red
Still, women who consider reducing their alcohol intake because of the link to breast cancer may be conflicted by other research suggesting that moderate consumption of alcohol can improve cardiovascular health and increase mortality.

Red wine, in particular, has been thought to have more health benefits than white wine or other types of alcoholic beverages, with laboratory studies even suggesting that resveratrol (a polyphenol more concentrated in red wine than in white) has an anticarcinogenic effect on the mammary tissues of rats. But cabernet lovers will be disappointed to learn that those benefits do not appear to extend to breast cancer risk in human subjects.

In a population-based case-control study designed primarily to look at the effect of beverage choice on breast cancer risk, Seattle researchers found that risk of breast cancer was not significantly different in wine drinkers than in those who drank other alcoholic beverages, nor in those who drank only red or only white wine.

That study found that consumption of more than 14 drinks per week was associated with a 24% increase in breast cancer risk (Cancer Epidemiol Biomarkers Prev 18:1007-1010, 2009).

“It’s clear from our study that alcohol consumption overall increases breast cancer risk,” said Polly A. Newcomb, PhD, MPH, head of cancer prevention at the Fred Hutchinson Cancer Research Center in Seattle and lead author of the study.

“If (a woman) chooses to drink red wine, she should do it because she likes the taste, not to reduce her risk of breast cancer,” Dr. Newcomb stated.

What’s excessive?
Many questions about alcohol and breast cancer risk remain unanswered, including the significance of binge drinking, historical vs current drinking patterns, and the effect of alcohol consumption on the risk of secondary cancers in survivors.

In addition, given the acceptance of alcohol in society, there is the question of whether statistics about breast cancer risk are realistically going to lead women to change their drinking habits.

“My feeling is that alcohol is a fairly well-established risk factor, and people should be counseled not to drink excessively. The question is, what’s excessive?” said Julia Knight, PhD, who has studied breast cancer risk factors, including alcohol (Am J Epidemiol 169:962-968, 2009).

Dr. Knight is a senior investigator at the Samuel Lunenfeld Research Institute in Toronto.

“I don’t feel that everyone should stop drinking tomorrow, which is not how I feel about smoking,” she said. “My advice to people is all things in moderation. That sounds like something your grandmother might have said, but I think there really is some truth to it.”