Video: Breast cancer?s magic bullet?

>>> we're back now with big news in the fight against breast cancer . coming out of a major cancer conference this weekend in chicago . more than 40,000 doctors meeting to discuss new break-throughs. tonight we're learning about a new drug that doctors and scientists hope could help about a quarter of the 230,000 women diagnosed with breast cancer in the u.s. each year. our report tonight from our chief science correspondent, robert bazell .

>> reporter: it is a new kind of drug. the so-called magic bullet that attacks a type of breast cancer while preserving quality of life .

>> anytime that we see a drug that can improve patient survival, improve their quality of life , and have few toxicities, we get so excited about that.

>> reporter: one of almost 1,000 women in the study out today. all had advanced breast cancer . it is especially aggressive. the standard treatment is a custom-made antibiotic called herceptin. the new drug called t-dm1 has a toxin that attaches to the cancer cells . delivering the poison directly, sparing the healthy cells and elem nating the need for additional chemotherapy. after two years, 65.4% of the women on t-dm1 were alive compared to 47.5% of those on the standard treatment . the doctors at the convention here in chicago are impressed enough with those results, they expect they're likely to get much better when the drug is given to women with much less advanced breast cancer . and because of the toxin only goes into the cancer, the side effects are relatively mild compared to the standard chemotherapy.

>> i don't feel sick. my insides don't feel raw. my fingernails are not turning black and i'm not losing my fingernails. and i'm able to live a very normal life .

>> reporter: dr. kimberly blackwell was the head researcher.

>> for 20 years we thought about this idea, if we could just kill cancer cells without hurting the patient faced with cancer.

>> reporter: experiments are under way to find other so-called magic bullets . for breast and many kinds of cancer. robert bazell , nbc news, chicago .

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