FDA Delays Decision on Ascendis Pharma's Dwarfism Drug, Impacting Competitive Landscape

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 Review and Clinical Implications

Ascendis Pharma's TransCon CNP, a once-weekly prodrug of C-type natriuretic peptide (CNP) designed to accelerate growth in children with achondroplasia, was initially granted priority review by the FDA. The delay stems from information filed by Ascendis on November 5, 2025, concerning the post-marketing requirement (PMR) protocol.

CEO Jan Mikkelsen stated that the FDA's request for a revised PMR protocol was "the lone item for discussion at our late-cycle meeting." This singular focus has been interpreted positively by TD Cowen analysts, who continue to expect approval despite the unexpected delay.

The analysts noted, "Based on the absence of a request for clinical data, the FDA is likely comfortable with the efficacy and safety seen in Ascendis' phase 3 trial." They speculate that the delay may be partly due to recent staffing cuts at the FDA, affecting review timelines.

Market Positioning and Competitive Landscape

If approved, TransCon CNP will enter the market as a direct competitor to BioMarin's Voxzogo, currently the only FDA-approved treatment for achondroplasia. Both drugs function as CNP analogs, but TransCon CNP's weekly dosing schedule could provide a significant advantage over Voxzogo's daily injections.

Analysts from TD Cowen have highlighted that phase 3 data for TransCon CNP and Voxzogo appear similar. However, they suggest that Ascendis' product may gain an edge due to its less frequent dosing regimen and the absence of hypertension as a side effect.

BioMarin, aware of the impending competition, is not resting on its laurels. The company recently shared phase 1 data on a once-weekly successor to Voxzogo, with BioMarin R&D chief Greg Friberg, M.D., claiming that their new candidate achieved area-under-the-curve levels more than three times higher than other long-acting CNP formulations.

Potential Label and Market Impact

While Ascendis' phase 3 trial enrolled children aged 2 to 11 years, there is speculation about the potential for a broader label. TD Cowen analysts, citing the precedent set by Voxzogo's approval, suggest that the FDA might allow TransCon CNP use in older children, potentially extending to those 15 years and older.

The analysts emphasized the importance of treating older children, stating, "This is an important age group as the bone plates typically do not fuse until mid-teenage years." They speculate that the PMR might involve collecting registry data across various age groups while allowing for use in patients 2 years and older.

As the pharmaceutical industry awaits the FDA's decision, the potential approval of TransCon CNP could significantly reshape the treatment landscape for achondroplasia, offering patients and healthcare providers an alternative therapy with a more convenient dosing schedule.