AstraZeneca said it will pay USD 2.5 billion upfront, then a further USD 1.5 billion once Dutch-and US-based Acerta's experimental drug acalabrutinib obtains regulatory approval from US authorities or else by the end of 2018.
Acalabrutinib has shown promise in treating leukemia and also auto-immune diseases such as lupus.
AstraZeneca, which rejected a takeover bid from US giant Pfizer last year, is seeking to rebuild its portfolio of exclusive medicines amid intense competition from generic drugmakers.
The British group is pushing several new innovative treatments for respiratory diseases as well as diabetes and cancers.