DIANE SAWYER (ABC NEWS)(OC): Good evening. We have a giant headline to tell you about tonight about health. The topic? Breast cancer and alcohol, including wine. The results are in from the biggest study of its kind in history, by the American Medical Association.
DIANE SAWYER (ABC NEWS)(VO): 100,000 women followed over 28 years, and the conclusion?
DIANE SAWYER (ABC NEWS)(OC): Less than a drink a day, even a glass of wine with dinner, could change the risk of breast cancer. In whom and why? So, we asked ABC's Andrea Canning to break it all down for us tonight.
ANDREA CANNING (ABC NEWS)(VO): The new study out today found compelling evidence that having even a single glass of wine each day raises your risk of breast cancer.
DOCTOR OTIS BRAWLEY (AMERICAN CANCER SOCIETY): In the past we've known women who consume a lot of alcohol increase their risk of breast cancer. We actually thought that a small amount of alcohol was relatively safe for breast cancer.
ANDREA CANNING (ABC NEWS)(VO): The study of more then 100,000 women over a 28-year period shows just 3 to 6 glasses of alcohol a week can increase a woman's chances of breast cancer by 15%, less than a glass of wine per day. If you bump that number up to two a day, the risk goes to 51%.
ANDREA CANNING (ABC NEWS)(OC): Does it make you think twice about having that extra drink?
PEDESTRIAN (FEMALE): It might. But honestly, probably not.
PEDESTRIAN (FEMALE) If wine is going to give a person breast cancer, I would definitely change my habit.
ANDREA CANNING (ABC NEWS)(VO): Doctors believe as many as 11% of breast cancers are linked to alcohol consumption. The increased risk is caused by the way the body reacts to alcohol.
ANDREA CANNING (ABC NEWS)(VO): Drinking increases levels of estrogen in the body, fueling tumor creation and growth. So what do you do? Especially given the fact that we've heard in the past that moderate alcohol use has been found to help prevent heart attack and stroke.
DOCTOR OTIS BRAWLEY (AMERICAN CANCER SOCIETY): The increased risk of breast cancer is really dwarfed by the evidence of the decreased risk of cardiovascular disease.
ANDREA CANNING (ABC NEWS)(VO): Still, today's study is the most significant bit of evidence that every time you raise your glass, you might be raising your breast cancer risk. Andrea Canning, ABC News, New York.
DIANE SAWYER (ABC NEWS)(OC): Which brings us to ABC's Dr Richard Besser. So, Rich, are you confident of this? Is this going to be another study we see reversed in another couple of months?
DOCTOR RICHARD BESSER (ABC NEWS)(OC): You know, this is the best study yet on this question. It's not the first study, but it's the best study. And if you have family members, women in your family, who've died from breast cancer, there's not a lot you can do. But this says there's something you can do that could possibly reduce your risk. And that's stop drinking.
DIANE SAWYER (ABC NEWS)(OC): So you have looked at all the evidence. You think they are onto something here with all these studies?
DOCTOR RICHARD BESSER (ABC NEWS)(OC): I think they really are. I think they are.
DIANE SAWYER (ABC NEWS)(OC): Okay, let me ask you about the other thing we keep hearing, which is a little bit of alcohol, moderate alcohol, prevents heart disease and stroke.
DOCTOR RICHARD BESSER (ABC NEWS)(OC): Right.
DIANE SAWYER (ABC NEWS)(OC): So, how do you choose between the two?
DOCTOR RICHARD BESSER (ABC NEWS)(OC): Well, that's the catch. If you don't have that breast cancer risk, you have to remember that a small amount of alcohol, one drink a day or less has been shown in lots of studies to reduce your risk of heart disease. And you have to remember, 1 in 3 women are going to die from heart disease. Only 1 in 36 are going to die from breast cancer. So, it may be worth continuing to have that drink, if you don't have that increased breast cancer risk.
DIANE SAWYER (ABC NEWS)(OC): So start by taking a look at your risk factors and then decide which course you're gonna take.
DOCTOR RICHARD BESSER (ABC NEWS)(OC): And if you don't drink now, no one is saying to start drinking.
DIANE SAWYER (ABC NEWS)(OC): Right.
DOCTOR RICHARD BESSER (ABC NEWS)(OC): There are too many things that can go wrong with starting drinking. But look at your own risk factors and that should help you decide.
DIANE SAWYER (ABC NEWS)(OC): Okay, thanks, Rich. As we said this is a really big new study and big conclusions.