* Patients on Tecentriq plus chemo lived two months longer
* Roche aims for 'first-mover' advantage in SCLC
* Rivals Keytruda, Opdivo have overshadowed Roche drug (Adds comment from company, market reaction, comment from analyst)
By John Miller
ZURICH, Sept 25 (Reuters) - A drug cocktail with Roche's Tecentriq added two months to small-cell lung cancer patients' lives, according to a study, aiding the Swiss group's bid to win approval in a niche disease area before rivals that now dominate the immunotherapy market.
Patients with untreated extensive-stage small-cell lung cancer (SCLC), where cancer has spread, lived a median 12.3 months after getting Tecentriq plus chemotherapy.
That compared to 10.3 months for those on chemotherapy alone, data released on Tuesday at the International Association for the Study of Lung Cancer annual conference showed.
Roche had said in June that its IMpower 133 trial was positive, but had not given the scale of the benefit.
Tecentriq has trailed Merck's Keytruda and Bristol Myers Squib's Opdivo in revenue as those medicines beat it to market in other indications. Merck's drug also has more-convincing trial results in lucrative non-small-cell lung cancer (NSCLC), which hits some 85 percent of lung cancer patients.
Roche Chief Executive Severin Schwan hopes to re-invigorate Tecentriq's momentum by being first in smaller indications like SCLC, which accounts for 10-15 percent of lung cancer cases but has proven tougher to fight than NSCLC and where there are fewer options for patients.
Roche Chief Medical Officer Sandra Horning said the 403-patient study's data represent the "first clinically meaningful advance in the disease in over 20 years", adding Roche would seek regulatory approval as soon as possible.
Its shares rose 1.1 percent at 1400 GMT, ahead of the 0.8 percent rise of the benchmark Swiss Market Index.
Baader Helvea analysts have said a "first-mover advantage" in small cell lung cancer for Roche could add $1.5 billion to Tecentriq's peak sales.
Other companies are on Roche's heels.
Bristol-Myers Squibb is studying Opdivo mixed with another established immunotherapy, Yervoy, against SCLC after chemotherapy. It collected final data from some 900 patients earlier this month, according to clinicaltrials.gov.
Should Bristol's numbers, when released, match Roche's for Tecentriq, the Swiss company may not reap much commercial benefit despite having a modest head start, Zuercher Kantonalbank analyst Michael Nawrath said.
"We can't make an absolute comparison yet," Nawrath said. "If the data for Bristol's version is just as compelling, then Roche has a problem."
In addition to keeping a lid on costs, Schwan has pegged Tecentriq as a pivotal medicine in helping counterbalance $21 billion in revenue at risk with patent expirations on the Basel-based drugmaker's three top sellers, Rituxan, Herceptin and Avastin.
So far, however, Roche's medicine, which like the Bristol and Merck drugs helps take off the immune system's brakes, has largely played the part of commercial also-ran.
In the first half of 2018, Tecentriq chalked up 320 million Swiss francs ($333.7 million), while Keytruda and Opdivo sales were nearly 10-fold higher, with each at around $3.1 billion. ($1 = 0.9590 Swiss francs) (Reporting by John Miller; Editing by Michael Shields)