LONDON, May 8 (Reuters) - AstraZeneca, which is fighting a $106 billion bid approach from Pfizer, said on Thursday it had launched a final-stage study of a key new lung cancer drug that is being fast-tracked through clinical tests.

The British drugmaker had said last month it planned to start Phase III testing imminently with MEDI4736, which belongs to a class known as anti-PD-L1 treatments that boost the immune system.

AstraZeneca has accelerated the development programme for the medicine following encouraging results from initial Phase I trials, results of which will be presented at the May 30-June 3 American Society of Clinical Oncology conference in Chicago.

The company's pipeline of experimental cancer drugs is one of the lures for Pfizer, which also expects to make big cost and tax savings from a buying AstraZeneca.

"MEDI4736 is an important molecule in our immuno-oncology portfolio and its entry into Phase III clinical trials is further evidence of our commitment to invest in distinctive science in our core therapy areas and to rapidly progress our immuno-oncology pipeline," said global drug development head Briggs Morrison.

The so-called PACIFIC trial will involve 702 patients across more than 100 sites globally. The goal is to evaluate progression free survival and overall survival with MEDI4736 compared with placebo in patients with locally advanced, unresectable Stage III non-small cell lung cancer.

(Reporting by Ben Hirschler; Editing by Pravin Char)