* Roche seeking to catch cancer rivals
* Swiss company notches third combo trial win
* Still awaiting overall survival data (Recasts to focus on Roche's strategy, adds analyst comment)
By John Miller
ZURICH, March 20 (Reuters) - Roche's immunotherapy Tecentriq on Tuesday racked up a third trial win in combination with other cancer drugs, a boost for the Swiss drugmaker as it seeks to muscle in on space dominated by Merck and Bristol-Myers Squibb.
A late-stage study, called IMpower131, demonstrated Tecentriq mixed with chemotherapies carboplatin and Abraxane cut risk of disease worsening or death (PFS), compared with chemotherapy alone, in first-line treatment of patients with advanced squamous non-small cell lung cancer.
Roche is aiming to be the first to win regulators' blessing for an immunotherapy combination against this form of lung cancer, which accounts for 25-30 percent of lung cancer cases.
The trial will continue, as Roche awaits overall survival data it hopes will show its combination keeps people alive longer than standard chemotherapy. Overall survival is the gold standard when assessing a drug's effectiveness.
Roche has numerous trials of Tecentriq with other drugs as the Basel-based company seeks to make up ground against Merck's Keytruda and Bristol-Myers Squibb's Opdivo medicines, whose combined sales are more than 10-fold those of Tecentriq's 487 million Swiss francs ($512.42 million) in 2017.
This latest data, from the IMpower131 trial, marks the third time since December that Roche has demonstrated a benefit for patients getting a Tecentriq cocktail, including against other forms of lung cancer and kidney cancer.
"Squamous non-small cell lung cancer is difficult to treat and there have been limited new treatment options over the last few decades," said Sandra Horning, Roche's chief medical officer. "We look forward to seeing more mature overall survival data."
Roche shares rose 0.3 percent at 0900 GMT.
"We currently model $1.1 billion of peak sales for Tecentriq in this setting and have previously highlighted that a positive result from the trial could see 1 percent to 3 percent upside to earnings per share," said Ian Hilliker, a Jefferies analyst.
Even so, being first is no guarantee of success. Tecentriq beat others in bladder cancer but Roche's rivals soon caught up.
"One year later, all the competitors -- Merck, Bristol and AstraZeneca -- got the nod for bladder cancer as well and the revenue growth of Tecentriq began to suffer," Zuercher Kantonalbank analyst Michael Nawrath said.
Since immunotherapies like Tecentriq, Keytruda and Optdivo work in just a fraction of patients, all the companies are staking hopes on combinations with other drugs to boost their success.
The cocktails are proving worthwhile. Last month, Bristol-Myers said a key lung cancer combination trial met its main goal while Merck data for Keytruda in January sent its shares soaring.
$1 = 0.9504 Swiss francs Reporting by John Miller; Editing by Michael Shields and Jon Boyle