(Bloomberg) -- Belgian biotech company Galapagos NV lost about a third of its market value -- its biggest decline on record -- after the U.S. Food and Drug Administration failed to approve a rheumatoid arthritis treatment it’s developing with partner Gilead Sciences Inc.

The regulator is concerned about the benefit and risk profile of the treatment, filgotinib, and has requested more data before completing its review, the companies said in a statement Wednesday. The FDA’s decision drove Galapagos down as much as 33%, wiping more than 3 billion euros ($3.6 billion) off its market value.

The FDA’s failure to appprove the drug is a “major setback,” Peter Welford, an analyst at Jefferies, wrote in a note. Safety concerns could delay a U.S. approval until at least the second half of 2021, adding risk to the drug’s regulatory prospects elsewhere, according to Michael Shah, a Bloomberg Intelligence analyst.

The shares were 24% lower at 10 a.m. in Amsterdam.

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