FDA Delays Decision on Ascendis' Dwarfism Drug, TransCon CNP

The U.S. Food and Drug Administration (FDA) has extended its review period for Ascendis Pharma's dwarfism drug candidate, TransCon CNP, pushing the decision deadline from November 30, 2025, to February 28, 2026. This three-month delay comes as the agency requires additional time to review recently submitted information regarding post-marketing requirements.

Regulatory Update and Company Response

Ascendis Pharma CEO Jan Mikkelsen stated that the FDA's request for a revised protocol for the post-marketing study was "the lone item for discussion at our late-cycle meeting." The company had submitted the requested information on November 5, which the FDA subsequently deemed a major amendment, necessitating the extended review period.

Despite the delay, analysts at TD Cowen remain optimistic about TransCon CNP's approval prospects. They noted that the FDA's focus on post-marketing requirements suggests the agency is "likely comfortable with the efficacy and safety" demonstrated in the phase 3 trial.

Clinical Data and Market Positioning

TransCon CNP is a once-weekly prodrug of C-type natriuretic peptide (CNP), designed to accelerate growth in children with achondroplasia, the most common form of dwarfism. The drug's phase 3 trial enrolled children aged 2 to 11 years, showing promising results that position it as a potential competitor to BioMarin's Voxzogo.

Analysts speculate that the FDA might grant approval for TransCon CNP in a broader age group, possibly including children 2 years and older. This would be significant, as bone plates typically do not fuse until the mid-teenage years, allowing for a wider treatment window.

Competitive Landscape

If approved, TransCon CNP will enter a market currently dominated by BioMarin's Voxzogo, a daily injectable CNP analog. Ascendis' weekly dosing regimen and the absence of hypertension as a side effect could provide a competitive edge over Voxzogo.

However, BioMarin is not standing still. The company recently shared phase 1 data on a once-weekly successor to Voxzogo, with BioMarin R&D chief Greg Friberg, M.D., reporting that the new candidate achieved area-under-the-curve levels more than three times those of another long-acting CNP.

As the FDA review continues, the pharmaceutical industry watches closely to see how this potential new entry will shape the treatment landscape for achondroplasia.