Telix Pharmaceuticals (ASX:TLX) received a complete response letter from the US Food and Drug Administration (FDA) for the biologics license application for TLX250-CDx, an investigational positron emission tomography (PET) agent used to diagnose and characterize renal masses as clear cell renal cell carcinoma, according to a Thursday Australian bourse filing.

The letter said that the regulator identified deficiencies relating to the chemistry, manufacturing, and controls package of the agent. The FDA documented notices of deficiency issued to two third-party manufacturing and supply chain partners.

The regulator requested additional data to establish comparability between the drug product used in the ZIRCON phase three clinical trial and the scaled-up manufacturing process intended for commercial use.

The firm said that the submission remediation will begin immediately, and it will request a Type A meeting with the FDA to address the highlighted deficiencies. It plans to continue to provide patient access to TLX250-CDx through an FDA-approved expanded access program, subject to consultation with the regulator.

Its shares fell 19% in recent trading on Thursday, reaching the lowest point in over 52 weeks.