LONDON (Reuters) - AstraZeneca now expects a key lung cancer study of two immunotherapy drugs to produce overall survival results in the second half of 2018, rather than the first half.

The Phase III trial, known as Mystic, is testing Imfinzi on its own and in combination with tremelimumab, and the drugmaker noted in a brief statement on Monday that it was driven by clinical events among patients involved.

First results from Mystic disappointed investors last July when AstraZeneca's two drugs proved no more effective at stopping disease progression than chemotherapy, sending its shares tumbling.

(Reporting by Ben Hirschler, editing by Louise Heavens)