The medication was used on its own and in combination with tremelimumab, an antibody treatment, in patients with stage-IV cancer.
The phase III clinical trial showed there was no statistical advantage to using the new drug.
"We are encouraged to see that Imfinzi monotherapy activity is in-line with that of the anti-PD-1 class in previously-untreated patients with Stage IV non-small cell lung cancer; however, we are disappointed that these results missed statistical significance,” said AZ chief medical officer Sean Bohen.
“We remain confident in Imfinzi as the cornerstone of our IO [immuno-oncology] programme and continue to evaluate its potential in ongoing non-small cell lung cancer trials, including Imfinzi and Imfinzi plus tremelimumab in combination with chemotherapy."
It should be noted that Imfinzi is approved in more than 40 countries for patients with inoperable stage III lung cancer.
The latest trial was part of a batch of studies to assess just which forms of the disease the new drug is capable of treating.