Roche's bid to shield its ageing but lucrative oncology franchise from cheaper copies got a lift from a trial showing a new drug cocktail kept breast cancer patients alive longer.

Combining its drug Perjeta with Herceptin and chemotherapy after surgery cut recurrence of an aggressive type of early breast cancer or death compared to Herceptin and chemo, the Swiss pharmaceuticals giant said in a statement on Thursday.

Shares in the world's biggest maker of cancer drugs were 5.2 percent higher at 258 Swiss francs at 0959 GMT, although analysts advised caution given Roche gave few specifics. It pledged more details at a 2017 medical conference.

Herceptin, approved in 1998, is losing patent protection, exposing it to competition from a biosimilar version that Mylan and Biocon may introduce in Europe this year.

By showing the addition of Perjeta improved results over the previous regimen, Roche aims to make the case to regulators and doctors that it will keep more patients alive longer.

"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.

About a third of HER2-positive breast cancer patients have historically suffered a relapse after successful initial therapy. Herceptin and chemotherapy have helped keep cancer from returning in more than 80 percent of these patients.

With Aphinity, the goal was to show adding Perjeta would improve invasive disease-free survival rates significantly.

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Herceptin brought in 6.78 billion Swiss francs ($6.71 billion) last year, up 4 percent. Sales of Perjeta, which won the U.S. Food and Drug Administration's blessing in 2013, rose 26 percent last year to 1.85 billion francs.

With Aphinity's "commercially significant" outcome, Zuercher Kantonalbank analyst Michael Nawrath expects revenue of 9 billion francs from the Perjeta-Herceptin franchise by 2021.

Still, analysts from Baader Helvea told investors to "beware", as Roche released only the trial's positive headlines.

"We see the limited released information regarding the Aphinity study leading to potential confusion and recommend waiting until the dust settles," wrote Baader's Bruno Bulic.

The drugs are already approved in combination with chemotherapy for those suffering from metastatic disease, but Aphinity tested Perjeta's ability to keep tumours from returning in breast cancer patients after surgery.