Selective Estrogen Receptor Modulator Receives FDA Rare Pediatric Disease Designation for Treatment of Duchenne Muscular Dystrophy

The US Food and Drug Administration (FDA) has granted Rare Pediatric Disease (RPD) designation to (Z)-endoxifen (Atossa Therapeutics, Seattle, WA) for the treatment of people with Duchenne muscular dystrophy (DMD). According to a statement from Atossa Therapeutics, the new designation expands the clinical development program for (Z)-endoxifen, establishing a regulatory pathway that, if statutory requirements are met and the drug is approved, could allow eligibility for a Priority Review Voucher (PRV). (Z)-Endoxifen is an investigational oral selective estrogen receptor modulator/degrader (SERM/D) that is not currently approved for treatment in any indication.

RPD designation is reserved for investigational therapies intended to treat serious or life-threatening diseases that primarily affect individuals from birth to age 18 and meet criteria for rarity under the Federal Food, Drug, and Cosmetic Act. DMD is a progressive X-linked neuromuscular disorder caused by mutations in the dystrophin gene, with symptom onset typically in early childhood and progression to loss of ambulation, respiratory failure, and cardiomyopathy. According to Atossa Therapeutics, (Z)-endoxifen does not target specific exon defects, which may allow evaluation across a broader DMD population.

Source: Atossa Therapeutics. Atossa Therapeutics receives FDA Rare Pediatric Disease Designation for (Z)-endoxifen for Duchenne muscular dystrophy. PR Newswire. Published 11 December, 2025. Accessed 15 December, 2025. https://prnmedia.prnewswire.com/news-releases/atossa-therapeutics-receives-fda-rare-pediatric-disease-designation-for-z-endoxifen-for-duchenne-muscular-dystrophy-302638744.html