Clovis Oncology Inc said the U.S. Food and Drug Administration asked for additional clinical data on the effectiveness of its experimental lung cancer drug, rociletinib, which could delay its approval.
Clovis's shares slumped 69 percent in premarket trading on Monday. The company had a market value of $3.8 billion as of Friday's close.
Clovis said it expects the review of additional information will result in a delay of a potential approval.
A similar treatment from AstraZeneca, designed for patients whose disease has worsened after treatment with other therapies, won early U.S. approval on Friday.
(Reporting by Ankur Banerjee in Bengaluru; Editing by Savio D'Souza)