A new drug could be a game changer in the battle against breast cancer, a disease that's expected to be diagnosed in more than 265,000 Americans this year. It targets tumors with remarkable precision.

Dikla Benzeevi, 49, has been living with breast cancer for 17 years. As the cancer spread to her lungs, she tried 15 different drugs. Last year, her doctors suggested she join a trial of a new therapy targeted specifically at Benzeevi's disease, HER2-positive breast cancer that's metastatic.

"There's no new tumors and it's staying stable, which is a good sign," Benzeevi said.

HER2 is a gene that results in aggressive breast cancer and occurs in about 20% of patients with metastatic disease. Targeted therapies like Herceptin often stop working as the cancer becomes resistant.

Results of this trial were released at the San Antonio Breast Cancer Symposium and published in the New England Journal of Medicine. The drug, for now labeled DS-8201, was tested in 184 patients. Tumors shrank in 61% of the patients, and disappeared in 6%.

"This new drug works basically by selectively delivering high concentrations of chemotherapy directly to the cancer cells. It's essentially like a guided missile," said Dr. Ian Krop, one of the authors.

Cancer growth was halted for an average of 16 months, longer than what is usually seen with current therapies.

"Patients were able to get back on with their lives and not have to worry about the cancer so much while the drug was working," Krop said.

The drug came with serious side effects, including severe lung injury that caused four deaths, so moving forward, the safety of the drug is going to be a concern. But it has been so successful that the Food and Drug Administration has decided to fast track its approval process of the drug, which could make it available for use as early as next year.

Editor's note: This article has been updated. The side effects included severe lung injury that caused four deaths.