A new antibody-drug has shown promise in shrinking or halting the growth of breast tumours, say researchers.

The metastatic HER2-positive cancer had become resistant to standard therapies.

Lead researcher Dr Ian Krop from Dana-Farber Cancer Institute found that hybrid agent, called T-DM1, shrank tumours by 30 percent or more in 40 percent of women with confirmed HER2-positive cancers.

Another 13 percent had stable disease for at least six months, for a total clinical benefit rate of approximately 53 percent.

T-DM1 is comprised of the cell-killing drug DM1 and is chemically linked to the monoclonal antibody trastuzumab, which selectively binds to the HER2 growth signal receptor, which is highly overexpressed in HER2-positive breast tumours.

"The antibody binds to the HER2 protein on tumor cells and delivers the drug (DM1) selectively to them - but not to normal cells," Krop said.

"This allows us to deliver high doses of the chemotherapy directly to tumour cells. And at the same time, the antibody continues to block the HER2 growth signals," Krop added.

He said although patients experienced side effects that included nausea, fatigue and lowered platelet counts, these effects were typically mild and the drug in general was well tolerated.

The findings were presented at the 32nd annual CTRC-AACR San Antonio Breast Cancer Symposium. (ANI)