AstraZeneca's immunotherapy drug durvalumab has been approved by U.S. regulators to treat advanced bladder cancer in patients. The medicine, which will be sold under the brand name Imfinzi, is part of a new generation of drugs that stimulate the immune system to help fight cancer.

AstraZeneca, which has North American headquarters and 1,500 employees in Wilmington, is testing the oncology medicine to treat lung cancer. Clinical trial results in patients are expected this summer.

"This first approval for Imfinzi is an important milestone in our return to growth," said AstraZeneca chief executive officer Pascal Soriot.

The Food and Drug Administration granted accelerated approval to Imfinzi to treat advanced or metastatic urothelial carcinoma, the most common form of bladder cancer, in patients whose disease has progressed despite chemotherapy.

The medicine is being tested on its own, and in combination with another immune system-boosting therapy called tremelimumab, in numerous cancers.

The approval comes as AstraZeneca has lost revenue due to patent expirations and generic competition for some of its blockbusters treatments, including schizophrenia drug Seroquel XR and COPD drug Symbicort.