And today abc news has gone pink across every broadcast saluting breast cancer awareness month and the search for a cure. Tonight we're also asking about prevention, specifically which women get the... See More
And today abc news has gone pink across every broadcast saluting breast cancer awareness month and the search for a cure. Tonight we're also asking about prevention, specifically which women get the least breast cancer and why. Abc's chief medical editor dr. Richard besser brings us the answer. Reporter: Ask mao in the chinese country side, a perfect example if you eliminate breast cancer risks. I have heard of it but i don't know anyone who has ever had it. Rural chinese women have the lowest rates in the world. She eats mostly rice and vegetables, little meat and fat which lowers her risk. A healthy weight and exercise lower it more and her days are filled with exercise. We are working all the time and we sweat every day. That's why we're so healthy. We sweat so much. Reporter: Add this. Mao had a child before she was 30 and she breast fed, both protect her from best cancer. Here's what it looks like to have the lowest risk in the world. If chinese women like mao moved to the united states studies show that within a generation her daughters would have the same risk as an american woman. Another population as an intriguing protection. Debbie howe has it. It's because she's blind from birth. Why would that protect against breast cancer? No light has never reached her retina and her melatonin is scheduled. Some studies link this to lower best cancer. Keeping a regular sleep schedule may protect you. Two populations that raise hope that prevention really is possible, that every woman can lower her risk. There is another source of hope, a vaccine. Yes, scientists are at work on vaccines against breast cancer, they're being tested here at walter reed medical center. What have you seen so far? From early studies we really observed they cut the recurrence risk in half. Reporter: It works like any vaccine works, delivering a small protein found in cancers so the immune system can respond to it and kill off cancer krels. If this works the hope is to come up with a vaccine to prevent breast cancer in the first place. Some would say that's a pipe dream. Do you agree? No. I think it's within reach. Reporter: American women like mao could some day be able to say I've heard of breast cancer but I don't know anyone who has ever had it. Wouldn't that be a dream. A vaccine within reach? When and could it be for everyone? They're finish enrolling 1,000 women in this trial and in three years they'll know whether it prevents breast cancer from coming back. The question from there is can it prevent it in the first place. I want to go back to the two groups of women you showed us. What does this teach us? How radically different is their rate of breast cancer than everyone else's. It's one tenth of rate of women in this country. We can learn from their behaviors. That's what pink is all about to reduce breast cancer in women here. Thanks so much. We've set up a special website. Abcnewsgoespink.Com with resources and information for americans with breast cancer. Go there, take the pink pledge, pay tributes to loved ones b badling the disease. Information always the best weapon.
This transcript has been automatically generated and may not be 100% accurate.