AstraZeneca PLC said a preclinical data set from one early-stage study supporting the development of acalabrutinib for cancer were falsified, adding that there are no risks for patients.

The company said a former Acerta Pharma employee acted alone to falsify the preclinical data set provided through external collaborations, but the "isolated issue" had no effect on the integrity of the drug.

The "data integrity issue" pre-dated AstraZeneca's $4 billion investment in Acerta Pharma in 2015.

In August, the U.S. Food and Drug Administration granted breakthrough therapy designation to acalabrutinib to treat patients with mantle cell lymphoma, a rare type of blood cancer.