Combining experimental antibody drug pertuzumab with Herceptin, an antibody first approved in 1998, and chemotherapy shrank tumors in nearly half of newly diagnosed breast cancer patients treated in a clinical trial.

Both of the antibody drugs are made by Roche Holding AG.

The 417 women in the midstage trial received four cycles of therapy before they underwent surgery.

The three-drug combination eradicated tumors in 46 percent of the patients, which is 50 percent more than was seen with the standard therapy of Herceptin plus chemotherapy, Dr. Luca Gianni, director of medical oncology at the National Cancer Institute in Milan, Italy, and the trial’s lead investigator said in a statement.

He also said combining the two antibody drugs alone eliminated the tumor in 17 percent of cases.

The study results were presented on Friday at the San Antonio Breast Cancer Symposium.

Both antibodies are designed to block the function of HER2, a protein produced by a specific gene with cancer-causing potential that is generated in about 25 percent of breast cancers. Because the drugs bind to different regions of the HER2 receptor, researchers aim for more complete blockage of the pathway.

Researchers said the combination therapy was not associated with a significant increase in side effects or cardiac risk.

Investigators are working on a follow-up trial to see how well the three-drug combination works for women who have already undergone surgery to have their breast cancer tumors removed.

Results from a pivotal trial looking at the combination of pertuzumab, Herceptin and chemotherapy as a first-line treatment in people with HER2-positive breast cancer are expected by the end of next year.

U.S. sales of Herceptin last year were $1.4 billion, while global sales were 5.26 billion Swiss francs ($5.33 billion).

$1 = 0.9863 Swiss franc

(Reporting by Deena Beasley, editing by Matthew Lewis)

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(Reuters)