A doctor points to a breast cancer tumor on an X-ray: After two years, 65 percent of the breast-cancer patients who received a new drug treatment called T-DM1 were still alive versus 47 of a control group administered standard treatment.

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esearchers are excited about a new cancer therapy that explicitly targets breast cancer cells while leaving healthy ones alone. The experimental "smart bomb," which attaches directly to tumors before killing them, is being hailed as "a major step forward" in the fight against cancer and could potentially reach the market within a year. Here's what you should know about the breakthrough:

Why is it called a "smart bomb"?
The treatment, referred to by doctors as T-DM1, combines two proven therapies to blast cancer cells: The drug Herceptin, a gene-targeted therapy sometimes used on patients whose tumors overproduce a specific protein, and a cancer-blasting form of chemotherapy so poisonous that it can't be administered alone. The two are bonded together by a chemical that unleashes when it comes into contact with breast cancer cells, delivering a potent payload that — unlike other cancer-fighting treatments — leaves healthy cells out of harm's way. Hence, T-DM1's "smart bomb" moniker.

How effective is it?
About 1,000 women with advanced breast cancer were given the drug. After two years, 65 percent of the women who received T-DM1 were still alive, versus 47 percent of a control group that was given standard treatment. More tests are necessary, however, because the margin was just below the rigid criteria cancer researchers use before declaring a new treatment a winner. 

Why is this such a breakthrough?
It's the first study to prove that tumors can be precisely targeted with an antibody, minimizing uncomfortable side effects. "People don't lose their hair, they don't throw up. They don't need nausea medicines, they don't need transfusions," study leader Dr. Kimberly Blackwell of Duke University tells The Associated Press. 

When might T-DM1 become available?
The drug's parent company, Roche, plans to file for FDA marketing approval in the U.S. and Europe by the end of the year. Shanu Modi, a New York breast cancer oncologist, who was not involved in the study, tells Bloomberg Businessweek that if T-DM1 is approved, "it is going to be rapidly taken up by the oncology community. For sure, I will be using a lot of it." 

Sources: Associated Press, Bloomberg Businessweek, Wall Street Journal