* Data shows Tecentriq helped breast cancer patients
* Survival data is immature, but Roche optimistic
* Trailing rivals, Roche seeking immunotherapy niches (Adds comments from lead study author, details on PD-L1 subgroup)
By John Miller and Ludwig Burger
ZURICH/MUNICH, Oct 20 (Reuters) - An immunotherapy cocktail from Roche helped slow an aggressive type of breast cancer where new treatments have proven elusive, offering positive news for the Swiss drugmaker as it chases medicines produced by its rivals.
Trial data released on Saturday shed light on the treatment of triple-negative tumours, which affect 15 percent of breast cancer patients, typically affecting younger-than-average women.
Tecentriq's benefit was shown to be greatest among the roughly 40 percent of trial participants who had high levels of a protein known as PD-L1, which helps tumours avoid immune system detection.
Those women lived a median 7.5 months without their disease worsening (PFS) with Roche's Tecentriq plus chemotherapy as an initial treatment, compared with 5 months for those getting chemotherapy alone, which is the current treatment standard.
Peter Schmid, clinical director of St. Bartholomew's Breast Cancer Centre in London and the study's lead author, said the results "will change the way triple-negative breast cancer is treated".
"All the benefit was observed in the PD-L1 positive sub-group... We have a very targeted treatment and a targeted population," he added.
Overall survival (OS) data from the IMpassion 130 study is not yet mature, but Roche Chief Medical Officer Sandra Horning told Reuters she had reason for optimism.
Patients getting the Tecentriq cocktail lived a median 21.3 months, so far, compared to 17.6 months for those on chemotherapy, she said.
Horning said the results offered new hope for people struggling with a difficult disease where patients and doctors desperately need new treatment options.
"It's really extraordinary to see a survival benefit of any kind in triple-negative breast cancer," she said. "We're quite excited about the degree of effect."
Roche has filed with regulators for approval.
Triple-negative tumours have no hormone receptors or HER2 receptors, so patients do not benefit from hormone therapy or HER2-targeting drugs like Roche's $7 billion-per-year blockbuster Herceptin or GlaxoSmithKline's Tykerb.
Roche in July announced the 902-patient study had showed adding Tecentriq to chemotherapy boosted outcomes, but the specific data were released at the annual congress of the European Society for Medical Oncology in Munich on Saturday.
With Roche's Tecentriq trailing immunotherapies from Merck and Bristol-Myers Squibb in the main form of lung cancer, Chief Executive Severin Schwan is pursuing smaller but still lucrative treatment areas where he can gain an approval head start.
So far, Tecentriq's sales are up 50 percent over the first nine months to 524 million Swiss francs ($528 million), but that is a fraction of sales generated by blockbuster checkpoint inhibitors from Merck's Keytruda and Bristol's Opdivo.
The less common small-cell type of lung cancer also offers an opportunity for Roche to be first to win the blessing of the regulators.
"Roche has more of a niche approach and is seeking to have clearly defined markets with dedicated studies," Gregoire Biollaz, fund manager at Pictet Asset Management, told Reuters.
Roche, the biggest maker of cancer drugs, needs Tecentriq to be a success. Roche's three biggest cancer drugs Avastin, Herceptin and Rituxan, earn $21 billion in annual sales, but patent expirations are already exposing them to competition from cheaper copies made by rivals.
Rivals Merck and Bristol-Myers Squibb are testing their own immunotherapy combinations against triple-negative disease, including with partners.
$1 = 0.9929 Swiss francs Editing by Edmund Blair and Adrian Croft