* Tecentriq drug cocktail cuts risk of disease progressing pct
* Drugmaker to file for expanded approval with latest data
* Analysts see drug sales topping $4.6 bln by 2023 -Reuters poll (Adds analyst comment, updates share price)
ZURICH, Dec 7 (Reuters) - Adding Roche's immunotherapy Tecentriq to older drugs doubled the percentage of lung cancer patients who survived a year without their disease advancing, an outcome some experts labelled unprecedented.
Thirty seven percent of patients in a closely watched clinical trial who received Tecentriq, Avastin and chemotherapy reached the one-year mark without their cancer progressing (PFS), according to data released on Thursday.
For patients getting only Avastin and chemotherapy, that fell to 18 percent.
Roche's announcement in November that its Impower 150 trial had broadly succeeded in first-line lung cancer patients helped spur a one-day, $12 billion rally in the Basel-based drugmaker's shares.
Thursday's release of specific numbers at a European Society for Medical Oncology meeting in Geneva could further fan investor optimism that the Swiss drugmaker is gaining on rivals Merck & Co and Bristol-Myers Squibb.
Roche Chief Executive Severin Schwan sees an opportunity to leap-frog ahead as competitors still await their own lung cancer combination trial results.
"This is very, very promising," Dr. Solange Peters, the head of Medical Oncology at the Centre Hospitalier Universitaire Vaudois in Lausanne, Switzerland, said on the latest results.
"Doubling PFS (progression-free survival) at one year is something we have not seen with any targeted therapy in unselected patients to date."
In a second significant trial result released Thursday, Roche posted interim data from its recently approved haemophilia drug Hemlibra dosed every four weeks, saying results were consistent with previous studies of the medicine dosed once a week or every two weeks.
Roche said it would submit the results from both studies to regulatory authorities around the world.
The Swiss company's shares initially rose more than 1 percent in Zurich, but retreated and were flat at 0900 GMT.
Some said Thursday's release, while positive, still leaves investors with too little information to make a full assessment of Tecentriq's potential against rivals' medications.
For instance, while Roche said the impact on overall survival suggested by the study was "encouraging," the numbers will not be ready for formal release until mid-2018. Comparisons to other immunotherapy combination trials are also difficult.
For instance, Merck's Keytruda cocktail won U.S. approval for treatment of first-line lung cancer in May based on a much smaller study involving just 123 patients, tiny compared to Roche's 1,202 person study.
"Impower 150 is one important piece of a complex, still largely incomplete, puzzle," wrote Bernstein's Tim Anderson. "This gives us a snapshot of the data, but not the complete picture, meaning our assessment here may change."
Roche is counting on $150,000-per-year Tecentriq to help replace revenue from its $20 billion-per-year trio of Avastin, Herceptin and Rituxan whose patents have expired or will shortly, exposing them to cheaper competition.
According to estimates collected by Reuters, Tecentriq annual sales are seen topping $4.6 billion by 2023.
Lung cancer is easily the biggest oncology market, with about 220,000 people in the United States due to be diagnosed this year and 155,000 seen dying from the disease often caused by smoking.
In Roche's study, patients getting Roche's immunotherapy survived an average of 8.3 months without their disease getting worse, only modestly better than the PFS of 6.8 months for those getting chemotherapy and Avastin.
Analysts focused more on the 38 percent reduction in risk of disease progression or death in the Tecentriq group, which was within the range they have said would signify a robust result, helping cement Tecentriq as a strong competitor.
"We see the Impower 150 outcomes sufficient for Roche to submit a robust data package to the health authorities and very likely obtain a marketing authorization in the U.S. by mid-2018," wrote Bruno Bulic, a Baader Helvea analyst with a "buy" rating on Roche shares.
Roche said Tecentriq performed even better in a group of patients who expressed a specific biomarker called "Teff" that the company thinks may help identify people who may respond best to immunotherapy. It noted a 49 percent risk reduction and PFS at 11.3 months for the Tecentriq group versus 6.8 months for those patients treated with only Avastin and chemotherapy.
Roche said serious adverse events were seen in 25.4 percent of patients receiving the Tecentriq combination compared with 19.3 percent in the Avastin-chemo group.
Tecentriq is already approved in bladder cancer treatment and for lung cancer patients who have failed chemotherapy.
(Reporting by John Miller; Editing by Ben Hirschler/Mark Potter/Susan Fenton)