(Reuters) -AstraZeneca ( AZN ) and its partner Daiichi Sankyo ( DSKYF ) have won approval from U.S. regulators for their precision drug Datroway to treat a type of lung cancer, marking the first approval of the therapy in this indication and expanding access for patients.

Datroway has been approved in the United States, the world's biggest pharmaceuticals market, to treat an advanced form of non-small cell lung cancer in adults who had received prior treatment, AstraZeneca ( AZN ) said on Tuesday, adding it was the first such therapy to get the greenlight there for treating lung cancer.

Datroway belongs to a class of medicines called antibody-drug conjugates, also known as "guided-missiles" because they are designed to target only cancer cells while sparing healthy cells, unlike conventional chemotherapy.

It works by targeting the TROP2 protein found on the surface of tumour cells of many types of cancer, and is already approved for treating a form of breast cancer. 

"This first approval of Datroway in lung cancer provides a much-needed option to patients with advanced EGFR-mutated lung cancer whose disease has become resistant to past treatments, regardless of the driving mutation," AstraZeneca ( AZN ) executive Dave Fredrickson said, referring to the specifics of the latest approval.

AstraZeneca ( AZN ) and Japan's Daiichi have a long-standing collaboration for developing cancer therapies, beginning first with Enhertu and then an agreement in 2020 to jointly develop and commercialize what is now Datroway in a deal worth up to $6 billion.

The Anglo-Swedish drugmaker on Tuesday said it would pay Daiichi $45 million in milestone-related considerations following the U.S. approval.