By E.J. Mundell
MONDAY, Sept. 29, 2014 (HealthDay News) -- Adding the drug Perjeta to a standard medication, Herceptin, may give women with a form of advanced breast cancer a significant boost in survival, a new study finds.
The finding is limited to patients with tumors called HER2-positive that have spread (metastasized). And experts say that this type of treatment-linked boost in survival -- an average of nearly 16 extra months of life -- is very rare in cancer research.
Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City, described the new findings as "extremely exciting."
"Great strides have been made in treating breast cancer, and it is particularly encouraging that we now have additional treatment to offer patients with HER2-positive metastatic disease that extends survival," she said.
"Treatment regimens continue to become more tailored to a patient's individual cancer, lessening unwanted side effects from drugs that may not be beneficial, and focusing on treatments that have been shown to improve outcomes for a specific tumor," added Bernik, who was not involved with the study.
However, certain HER2-targeted medications such as Herceptin and Perjeta (pertuzumab) aim to interrupt this process, curbing the tumor's spread.
According to the U.S. National Cancer Institute, about 20 percent of breast cancers are HER2-positive.
The study -- funded by drugmaker Genentech and presented Sunday at the European Society for Medical Oncology meeting in Madrid, Spain -- follows a positive report for Perjeta released in 2012. That trial suggested that patients with HER2-positive cancers might benefit, but more time was needed to discover just how big the benefit might be.
The study involved more than 800 women with advanced HER2-positive breast cancers whose illness had either never been treated, or who had returned for treatment after undergoing a different regimen. Patients either received a combination of three drugs -- Perjeta, Herceptin and docetaxel -- or Herceptin, docetaxel and a "dummy" drug (placebo). Patient outcomes were then tracked for a median of more than 4 years.
The researchers reported that people who took Perjeta along with the other two standard medications gained an average 15.7 months in survival (56.5 months versus 40.8 months). This was equivalent to a 32 percent reduction in the odds that the patient would die over the length of the trial, the authors noted.
"Adding Perjeta to treatment with Herceptin and chemotherapy resulted in the longest survival observed to date in a clinical study of people with HER2-positive metastatic breast cancer," study lead author Dr. Sandra Horning, chief medical officer at Genentech, said in a company news release. She called the survival boost "a magnitude of improvement we rarely see in clinical trials in advanced cancer."
However, there were some downsides to taking Perjeta, which was approved by the U.S. Food and Drug Administration in 2012 for use against breast cancer. The study found that women taking Perjeta had higher rates of diarrhea, rash and a lowering of white blood cell counts compared to women taking only Herceptin and docetaxel.
And the study found that -- for reasons that remain unclear -- Perjeta only slowed the progression or worsening of the disease by an average of about 6 months, even though it extended overall survival by much longer.
"This prolongation of survival is unprecedented, particularly in this group of patients with higher-risk disease," said one of the study investigators, Dr. Paula Klein, assistant professor of medicine, hematology and medical oncology at Icahn School of Medicine at Mount Sinai in New York City.
The drug comes with a hefty price tag, though. According to The New York Times, patients in the United States can expect a bill of about $5,900 for a month's supply of Perjeta.
That's in addition to the $5,300 monthly cost of Herceptin, the newspaper said. Klein labeled such costs the "financial toxicity" of new cancer drugs.
Experts note that studies presented at medical meetings are typically considered preliminary until published in a peer-reviewed journal.