Bristol-Myers Squibb's immunotherapy drug Opdivo extended kidney cancer survival rates by more than two years in a late-stage trial, setting it up to be used beyond melanoma and lung cancer. 

The U.S. company said in July the study was stopped early because its drug was more effective than Novartis' established product Afinitor, but detailed results were only disclosed at the European Cancer Congress in Vienna on Saturday.

The successful outcome means Opdivo is the first so-called immune checkpoint inhibitor drug to show an improvement in overall survival in patients with renal cell carcinoma (RCC), a common type of kidney cancer.

Opdivo is already approved for melanoma and lung cancer, with most attention focused on the big lung cancer opportunity. But analysts noted that RCC prevalence was twice that of melanoma, pointing to significant commercial upside.

Drugs like Opdivo work by targeting molecules that play an important role in the immune system's ability to recognize and attack tumors.

Padmanee Sharma of the U.S. MD Anderson Cancer Center, one of the lead researchers on the study, said patients taking Opdivo had a median overall survival of 25 months as compared to 19.6 months for those taking Afinitor.

A greater proportion of patients also had tumors that shrank in response to the Bristol drug than to the Novartis one, with an objective response rate of 25 percent for Opdivo against 5 percent for Afinitor.

"The results are significant and clinically meaningful to patients and healthcare professionals alike," Sharma said. "They are likely to change the treatment of patients with advanced kidney cancer, whose disease has progressed on prior treatment."

The findings were also published online in the New England Journal of Medicine.

Michael Giordano, Bristol's head of oncology development, told Reuters the company was working towards filing Opdivo for approval in kidney cancer "very quickly" but he declined to give a precise date for submission to regulators.

Analysts at Morgan Stanley believe Opdivo could be approved for the new use by early 2016 and the U.S. National Comprehensive Cancer Network might endorse its off-label in kidney cancer before the end of 2015.

Bristol is also a testing a combination of Opdivo and its drug Yervoy as a first-line treatment for kidney cancer.

Opdivo is a so-called PD-1 inhibitor that blocks a mechanism tumors use to hide from the immune system. It competes with Merck's Keytruda.

AstraZeneca, Roche and other drugmakers are also developing similar drugs known as PD-L1 inhibitors.