March 25 (Reuters) - Regeneron Pharmaceuticals ( REGN )

said on Monday the U.S. FDA has declined approval for its blood

cancer therapy for two forms of lymphoma, raising concerns over

the progress of ongoing confirmatory trials.

In its so-called complete response letter (CRL), the U.S.

Food and Drug Administration said it needed more data from

enrollments in dose-finding and confirmatory portions of trials,

delaying its decision on the drug.

The company was testing its experimental drug, odronextamab,

in multiple late-stage trials in patients with Follicular

lymphoma and Diffuse large B-cell lymphoma, the two most common

subtypes of non-Hodgkin lymphoma.

"To our knowledge, this is the first time the FDA has issued

a CRL for this reason," a Regeneron spokesperson said about the

decision by the FDA, which did not identify any issues with the

drug's clinical efficacy or safety, trial design, labeling or

manufacturing.

Shares of the company fell nearly 2% to $948.90 in premarket

trading. The company was looking to expand its oncology

portfolio with odronextamab, beyond its lone approved cancer

drug, Libtayo.

"While we acknowledge the general concerns that FDA has

about sponsors failing to complete their post-marketing

confirmatory trials, the relevant laws and regulatory guidances

do not lay out rigid criteria for assessing whether the progress

on a confirmatory trial is adequate to allow for an accelerated

approval," the Regeneron spokesperson said.