A new breast cancer drug from Roche has shown "unprecedented" survival benefits in a clinical trial, boosting prospects for its widespread use in women with an aggressive form of the disease.

Patients with a type of breast cancer known as HER-2 positive, which makes up about a quarter of all breast cancers, who were given Perjeta on top of older medicine Herceptin and chemotherapy lived 15.7 months longer than those on Herceptin and chemotherapy alone.

“The survival improvement of nearly 16 months ... is unprecedented among studies of metastatic breast cancer,” lead researcher Sandra Swain from the Washington Hospital Center told the European Society for Medical Oncology annual congress on Sunday.

Perjeta, which was approved by regulators two years ago, was tested in the Roche-backed study in more than 800 women with metastatic disease, whose breast cancer had spread to other parts of the body.

Researchers had previously reported the Perjeta drug regimen significantly extended progression-free survival, or the period of time patients live without their disease worsening, but the final overall survival data has taken longer to collect.

The median overall survival time was 56.5 months for those given Perjeta against 40.8 months for patients taking only the older drugs.

REMARKABLE RESULTS

Javier Cortes, another researcher on the study from the Vall D’Hebron Institute of Oncology in Barcelona, said the results were "remarkable" and suggested using Perjeta should be the standard of care for HER-2 positive breast cancer patients.

A favourable reaction from oncologist 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 is a costly drug and the multiple-drug regimen promises to strain budgets.

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.

Both Herceptin and Perjeta are antibodies designed to block the function of HER2, a protein produced by a cancer-linked gene. Pertuzumab binds to a different part of the same protein, which makes combining the two drugs extra effective.

The safety profile of Perjeta in the long-term analysis presented in Madrid did not reveal any new problems and was consistent with previous evidence, including Perjeta’s long-term cardiac safety.

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.