A combination of two Bristol-Myers Squibb immunotherapy drugs cut the risk of death by 37 percent in a key group of kidney cancer patients, data from a closely watched clinical trial showed on Sunday.

The news confirms the cocktail's utility in a hard-to-treat disease, following a rollercoaster ride.

The U.S. drugmaker reported three days ago it was ending the trial well ahead of schedule due to its early success in improving overall survival, despite earlier mixed results.

Now the scale of the benefit provided by the two immune system-boosting drugs has been disclosed to experts attending the European Society for Medical Oncology (ESMO) congress in Madrid.

In August, Bristol-Myers reported Opdivo and Yervoy failed to significantly outperform standard care in checking cancer progression, although there was a trend toward benefit.

The latest result is important for doctors and investors alike, not only because it opens up a new option for treating kidney cancer but also because it helps validate the idea of combining two different kinds of immunotherapy.

SUTENT COMPARISON

Opdivo works by blocking the activity of a protein called PD-1, while Yervoy tackles another called CTLA-4. AstraZeneca is combining two similar drugs in a large lung cancer trial that reported disappointing initial results in July.

In the study, the combination of Opdivo and Yervoy was compared to Pfizer's drug Sutent, a well-established treatment for renal cell carcinoma. Sutent is a so-called TKI drug that blocks signals in cancer cells.

Researchers found that it cut the risk of death by 37 percent in intermediate- and poor-risk patients, which was a main pre-specified endpoint of the study. It also improved overall survival in all patients, a secondary measure of success.

Significantly, the immunotherapy combination caused fewer serious side effects than Sutent, lead researcher Bernard Escudier of the Institut Gustave Roussy in France said.

He believes the efficacy and safety profile mean Opdivo plus Yervoy should become a new first-line standard of care for patients with advanced disease.

Maria de Santis of Britain's University of Warwick, who was not involved in the study, told reporters: "This data is clearly important and practice-changing and it challenges our former standard of care with TKI therapy."

Renal cell carcinoma is the most common type of kidney cancer in adults, accounting for around 100,000 deaths worldwide each year.

Bristol-Myers is a leader in the fast-growing field of cancer immunotherapy and Opdivo is expected to become one of the world's top-selling medicines. But the drugmaker has been under pressure in the past year after falling behind Merck due to Opdivo's failure to prolong survival in previously untreated lung cancer, the largest cancer market.