Roche hopes the important trial outcome will help shield its oncology franchise from cheaper copies.
"These results from the positive Aphinity study represent an important addition to the body of data for Perjeta in the treatment of people with HER2-positive early breast cancer," Sandra Horning, Roche's chief medical officer, said.
Analysts from Deutsche Bank have estimated around $2 billion in annual sales in 2018 hinged on the Aphinity trial's outcome.
Herceptin brought in $6.75 billion in sales last year for Roche but is losing patent protection, exposing it to competition from a biosimilar version that Mylan and its partner Biocon may introduce in Europe later this year.
By showing Herceptin, Perjeta and chemo helped people who had undergone surgery live longer without their disease returning compared with the previous regimen of Herceptin and chemotherapy, the Basel-based drugmaker aims to make the case for doctors to switch to this new combination.
Herceptin was initially approved in 1998, while follow-on Perjeta won the U.S. Food and Drug Administration's blessing in 2013.
The drugs are already approved in combination for those suffering from metastatic disease, but Aphinity tested Perjeta's ability to keep cancer from returning in women who had undergone surgery.
Roche has said its 2017 guidance of sales and profit rising at a low- to mid-single digit percentage rate was issued irrespective of the Aphinity outcome, but analysts including those at Jefferies contend this trial will likely be a catalyst for shares.
"We estimate a positive top line result could drive stock price upside of about 15-20 francs versus downside of about 25-35 francs if the study fails," Jefferies' Jeffrey Holford wrote earlier this year.
(Reporting by John Miller; Editing by Michael Shields)
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