* Roche mix cuts death risk in kidney cancer
* Bristol study last year had mixed results
* Roche's Tecentriq sales trail rivals' blockbusters
By John Miller
ZURICH, Feb 6 (Reuters) - Roche's Tecentriq mixed with an older drug cut the risk of death in kidney cancer, marking another win for the Swiss drugmaker's immuno-oncology (I/O) cocktail as it battles better-established medicines made by its rivals.
Tecentriq, paired with Roche's Avastin, cut risk of renal cell carcinoma advancing or death (PFS) by 26 percent in patients whose tumours expressed high levels of a protein believed to help avoid immune detection, the Basel-based drugmaker said on Tuesday.
Roche said the overall survival benefit in its IMmotion 151 trial looked encouraging, but that data was not yet mature.
Success of Roche's trial, so far, compares favorably with the mixed results in last year's study by Bristol-Myers Squibb for its Opdivo and Yervoy combination against kidney cancer.
"Today's results are good, as IMmotion 151 met the co-primary endpoint of PFS, while Bristol's CheckMate-214 missed," Bank Vontobel analysts wrote in a note to investors.
Roche shares fell 1.2 percent at 1350 GMT, less than the 1.8 percent drop of the Stoxx European Health Care Index.
This is the second time Tecentriq with Avastin has succeeded, after a separate study in December showed the cocktail helped lung cancer patients.
Still, Roche has an uphill fight to establish Tecentriq as a go-to immunotherapy amid a pack of immunotherapy combinations from rivals that have also scored recent trial wins.
Bristol reported on Monday that Opdivo and Yervoy boosted life expectancy in lung cancer patients whose tumours had many mutations.
Meanwhile, Merck's Keytruda immunotherapy plus chemotherapy aced a lung cancer trial last month.
So far, Tecentriq with its 487 million Swiss francs ($519.30 million) in sales in 2017 is still chasing Merck's Keytruda with $3.8 billion and Bristol's Opdivo with $4.9 billion.
The success of three different approaches against different cancers suggests doctors will face tough decisions over which cocktail to use, since tumours of the same organs can differ wildly from patient to patient.
"Physicians will have a challenge deciding which biomarker to use to and which therapeutic option to consequently prioritise," Barclays analyst Emmanuel Papadakis said.
With its medicine fighting to gain traction, Roche says understanding which immunotherapy combination works best remains a work in progress. The Swiss drugmaker has six Tecentriq trials to read out by July.
"As we approach the end of this year, we'll have a much clearer evidence base," Roche drugs division chief Dan O'Day said on Friday.
$1 = 0.9378 Swiss francs Reporting by John Miller; Editing by Edmund Blair