A drug used to treat advanced breast cancer has had what appears to be unprecedented success in prolonging lives in a clinical trial, researchers reported on Sunday.
Patients who received the drug — Perjeta, from the Swiss drug maker Roche — had a median survival time nearly 16 months longer than those in the control group.
That is the longest amount of time for a drug used as an initial treatment for metastatic breast cancer, the researchers said, and it may be one of the longest for the treatment of any cancer.
Most cancer drugs prolong survival in patients with metastatic disease for a few months at most. Metastasis means the cancer has spread to other parts of the body.
“We’ve never seen anything like this before,” said Dr. Sandra M. Swain of the MedStar Washington Hospital Center in Washington, the lead author of the study. “It’s really unprecedented to have this survival benefit.”
The results were being presented on Sunday in Madrid at the annual meeting of the European Society for Medical Oncology. Dr. Swain has been a paid speaker for the company.
Previous analyses of the clinical trial established that Perjeta, known generically as pertuzumab, increased survival by a statistically significant amount. But until now it was not known by how much, because patients had not been followed long enough.
Two experts not involved in the study, Dr. Edith A. Perez of the Mayo Clinic in Jacksonville, Fla., and Dr. Harold J. Burstein of the Dana-Farber Cancer Institute in Boston, said the results were impressive. “Usually we see two months of improvement,” Dr. Perez said.
Perjeta, like the better-known Roche drug Herceptin, or trastuzumab, blocks the action of a protein called HER2, which spurs the growth of some breast tumors. Perjeta is meant to be used with Herceptin for the roughly 20 percent of breast cancers characterized by an abundance of HER2.
Perjeta was approved by the Food and Drug Administration in 2012 and is already considered the standard of care in the United States.
Still, the results could lead to increased use of the drug. Only about half of the eligible women are being treated with the drug in the United States, according to Edward Lang Jr., a spokesman for Roche. And doctors say use is lower in many countries where cost is more of an issue.
In the United States, Perjeta costs about $5,900 a month and Herceptin about $5,300 a month, Mr. Lang said. He said Perjeta was priced lower than some other new cancer medicines because it has to be used with Herceptin. Some recently approved cancer drugs cost more than $10,000 a month.
Roche reported Perjeta sales of 388 million Swiss francs, or about $408 million, in the first half of this year, with about $250 million of that coming from the United States.
The trial, sponsored by Roche, involved 808 patients around the world with previously untreated HER2-positive metastatic breast cancer. Half of them received Perjeta, Herceptin and the chemotherapy drug docetaxel. The other half received Herceptin, docetaxel and a placebo in place of Perjeta.
The median survival time for those who received Perjeta was 56.5 months, or about four and a half years, compared with 40.8 months for those in the control group, a difference of 15.7 months. By another measure, known as the hazard ratio, use of Perjeta reduced the risk of dying 32 percent.
Use of Perjeta delayed the progression or worsening of the cancer only about six months in the trial. Experts said it was not clear why the drug extended lives so much longer than that.
Those receiving Perjeta had higher rates of diarrhea and rash and a lowering of white blood cell counts.
The labels for both Perjeta and Herceptin contain warnings that the drugs can cause cardiac dysfunction and heart failure. But in the study, patients who received Perjeta did not experience any more of these problems than those in the control group.
Dr. Perez and Dr. Burstein, the experts not involved in the study, said in separate interviews that they were also cheered by a nearly 41-month median survival in the control group.
When Herceptin was approved in the late 1990s, people taking that drug lived a median of about 25 months. The experts said doctors now use Herceptin for a longer time and can better manage patients.
"We've never seen anything like this before," said the lead author of a new study of a breast cancer drug that appears to have unprecedented success in prolonging lives.
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