May 29 (Reuters) - Merck ( MRK ) and Japan-based Daiichi

Sankyo ( DSKYF ) have withdrawn their U.S. application for an

experimental lung cancer treatment after it failed to prolong

patients' lives in a late-stage study, the companies said on

Thursday.

The drug, patritumab deruxtecan, belongs to a lucrative

class of targeted cancer therapies that work like "guided

missiles" by killing tumor cells while leaving healthy ones

unharmed.

The companies sought approval for the drug to treat

non-small cell lung cancer in patients who have failed two or

more prior lines of therapy and who had a specific gene mutation

leading to abnormal cell growth.

The U.S. Food and Drug Administration had declined to

approve the therapy last year due to issues with a third-party

manufacturing facility.

(Reporting by Mariam Sunny in Bengaluru; Editing by Shreya

Biswas and Devika Syamnath)