* Boost for drugmaker's prospects after Mystic trial setback
* Imfinzi improves progression-free survival by 11.2 months
* Tagrisso PFS 18.9 months vs 10.2 months with older drugs
MADRID, Sept 9 (Reuters) - Two AstraZeneca drugs tackling lung cancer in different ways delivered encouraging results on Saturday, helping the British group offset July's big clinical trial setback in the disease.
Particularly impressive was the success of the infused immunotherapy medicine Imfinzi in helping non-small cell lung cancer patients with inoperable disease that had advanced locally but not spread widely around the body.
Patients in a large clinical trial survived on average 16.8 months without their disease worsening when given the drug, against just 5.6 months for those on placebo.
Solange Peters of the Centre Hospitalier Universitaire Vaudois in Lausanne, who was not involved in the study known as Pacific, told Reuters the advantage of more than 11 months provided by Imfinzi was "absolutely amazing."
It is the first medicine to show superior progression-free survival in such patients. These individuals typically receive a combination of chemotherapy and radiotherapy, but only around 15 percent of them are still alive after five years.
Significantly, while there were more reports of toxicity in patients taking Imfinzi, the level of severe problems was similar in both groups.
"What we hear from the experts is that they think this is practice-changing," AstraZeneca's CEO Pascal Soriot told reporters.
AstraZeneca had already said that Pacific and another study called Flaura met their pre-defined goals, but the exact scale of the benefits were only disclosed at the European Society for Medical Oncology (ESMO) congress in Madrid.
Analysts believe using Imfinzi in so-called stage III lung cancer opens up an annual sales opportunity worth around $2 billion. The company also has an important lead of two to three years over rivals in this particular area.
However, this market is still smaller than for advanced lung cancer, where a combination of Imfinzi and tremelimumab failed to work as hoped in the Mystic trial.
Early success in Mystic would have given AstraZeneca the chance to establish the first immunotherapy combination in advanced lung cancer, ahead of rivals Bristol-Myers Squibb , Roche and Merck.
The Flaura trial, meanwhile, demonstrated the ability of AstraZenecas new pill Tagrisso to hold lung cancer at bay in patients with a certain genetic mutation that is particularly common in Asia.
The study showed Tagrisso, which AstraZeneca has already predicted will become a $4 billion-a-year seller, was significantly better than older medicines that act in a similar way.
Patients on Tagrisso went 18.9 months on average before their disease worsened, against 10.2 months for those given either Roche's Tarceva or AstraZeneca's Iressa.
ESMO spokesman Enriqueta Felip of Spain's Vall dHebron Institute of Oncology said Tagrisso's edge over older medicines and its good tolerability meant it should be considered a new first-line treatment option.
AstraZeneca is now in discussions with global health authorities about seeking marketing approval to extend the use of both Imfinzi and Tagrisso, based on the Pacific and Flaura data. (Reporting by Ben Hirschler; Editing by Mark Potter)