The drug works like a smart bomb -- traveling all over the body until it reaches the cancer cells.
Clinical trials show a powerful drug cocktail called TDM-1 can target cancer cells specifically without affecting non-cancerous cells and tissue.
Out of 1,000 women who took it, half saw their cancer stabilize. They also had fewer side effects than with standard chemotherapy.
The drugs will not be available until next year, but experts say cancer patients should talk to their oncologists about whether they are eligible for clinical trials.