Looking at the study results a different way, the risk of dying was reduced by 32 percent for women who received the Perjeta regimen compared to those who got Herceptin and chemotherapy.
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While both Perjeta and Herceptin have side effects, including rash, diarrhea and a potentially adverse impact on heart function, using the two drugs together did not make these issues any worse.
"I think these data are really compelling," said Eric Van Cutsem of the University of Leuven, who was not involved in the research. "When you see in breast cancer such a big change in survival with not a lot of cardio-toxicities then that is really practice-changing."
Swain and Javier Cortes, another researcher on the study from the Vall D'Hebron Institute of Oncology in Barcelona, said the results suggested using Perjeta should now be the standard of care for HER2 positive breast cancer patients.
A favorable reaction from oncologists will underpin expectations of strong sales for Perjeta, which analysts currently expect to sell $3.1 billion a year by 2018, according to consensus forecasts compiled by Thomson Reuters Cortellis.
But it poses a challenge for healthcare providers, since Perjeta and Herceptin are costly injectable drugs and the multiple-drug regimen promises to strain budgets.
In the United States, the monthly price of Perjeta is approximately $5,900, while Herceptin costs around $5,300, a Roche spokeswoman said. Prices in Europe are lower.
For Roche, Perjeta is an important new product that should help defend its position in breast cancer, following the success of Herceptin, which was first approved in 1998.
The company said the latest data would be submitted to regulatory authorities around the world for inclusion in the prescribing information for Perjeta.
The Swiss drugmaker also has another related drug called Kadcyla, which is also being tested in combination with Perjeta. Some analysts believe Kadcyla's prospects could be curbed if results from that combination are not better than the impressive findings reported this weekend.