Bristol immune drug shows strong effect in melanoma study

* 32 percent response rate in patients treated with Opdivo

* 95 percent of responders still benefiting after 6 months

* Lung cancer results with Opdivo expected later in year (Adds detail on forthcoming lung cancer study findings)

By Ben Hirschler

MADRID, Sept 29 (Reuters) - Bristol-Myers Squibb's immunotherapy drug Opdivo produced markedly improved response rates with fewer toxic side effects compared to chemotherapy in a major melanoma study, underscoring its potential as a new treatment option.

The data has been keenly awaited since this is the first presentation of results from a pivotal Phase III clinical trial of a promising new class of drugs designed to help the body's own immune system fight cancer.

In the study, involving people with advanced melanoma, 32 percent of patients saw their tumours shrink when given Opdivo against 11 percent of those treated with conventional chemotherapy drugs.

Importantly, the duration of response was also much longer. Patients on chemotherapy typically responded for 3.6 months, whereas 95 percent of those who responded to Opdivo were still benefiting after six months and the median duration of response was not reached.

Patients in the study had previously been treated with the company's Yervoy immunotherapy, which works in a different way to take natural brakes off the immune system.

"I was very nicely surprised," said Jeffrey Weber of the Moffitt Cancer Center in Florida, who presented the results at the European Society of Medical Oncology annual congress on Monday.

"A 32 percent response rate with the majority staying in remission past six months is probably going to turn into a very impressive level of survival," he said. "I hope this is the death knell for chemotherapy in melanoma."

Opdivo, or nivolumab, is part of a promising new class of drugs designed to block a protein known as Programmed Death receptor (PD-1), or a related target known as PD-L1, used by tumours to evade the immune system's disease-fighting cells.

Industry analysts are waiting next to see how Opdivo performs in another Phase III trial in lung cancer, for which they expect results in the fourth quarter of 2014. Since non-small lung cancer is a much bigger market than melanoma, that trial is viewed as critical to the drug's commercial outlook.

Some investors are nervous about Opdivo's lung cancer prospects but Weber, for one, is upbeat. "It is highly likely that the lung data will be positive," he told Reuters.

Opdivo became the first PD-1 inhibitor to receive regulatory approval anywhere in the world in July when Japanese regulators gave it a green light, although it has been beaten to market in the United States by Merck & Co's rival Keytruda, which was approved earlier this month.

On Friday, Bristol-Myers said the U.S. Food and Drug Administration had granted Opdivo a priority review and a decision on approval was due by the end of March.

Companies such as Roche and AstraZeneca (NYSE: AZN - news) are also developing PD-1 pathway drugs for a variety of cancers, including lung cancer. Some analysts expect the new class could generate more than $30 billion in annual sales worldwide by 2025. (Editing by Michael Urquhart, editing by Louise Heavens)