On August 19, 2026, the U.S. Food and Drug Administration (FDA) approved Regeneron Pharmaceuticals' Pasatru (garetosmab-grts), marking the agency's 33rd novel therapeutic approval of 2026 and establishing the second-ever FDA-approved disease-modifying therapy for fibrodysplasia ossificans progressiva (FOP).
FOP is an ultra-rare, severely disabling genetic disease affecting an estimated 900 diagnosed individuals worldwide per Regeneron, with roughly 300 in the United States according to the most rigorous prevalence estimate to date (0.88 cases per million; Pignolo et al., Orphanet Journal of Rare Diseases, 2021). Characterized by painful episodic soft-tissue swelling ("flare-ups") and progressive heterotopic ossification (HO)—the permanent transformation of muscles, tendons, and ligaments into extra-skeletal bone—FOP progressively immobilizes joints, fuses the ribcage, restricts pulmonary function, and leads to cumulative, irreversible functional decline.
For biopharma commercialization teams, specialty pharmacies, hospital pharmacy and therapeutics (P&T) committees, and health plan medical directors, the arrival of Pasatru introduces a critical clinical, economic, and operational inflection point. Pasatru arrives with an annualized Wholesale Acquisition Cost (WAC) averaging $1.4 million per year (spanning a company-stated, weight- and dose-dependent range of approximately $693,000 to $2.1 million, per a Regeneron spokesperson quoted by Managed Healthcare Executive), positioned against Ipsen's incumbent oral agent Sohonos (palovarotene), which launched in 2023 at an annual WAC of $624,000.
Yet behind the headline pricing gap lies a fundamental divergence in regulatory label scope, pivotal trial endpoints, boxed-warning structures, administration channels, and launch reimbursement dynamics.
The launch snapshot: Pasatru vs Sohonos at a glance
To understand how Pasatru alters the clinical and commercial landscape of FOP, market-access and clinical teams must evaluate the two approved products across regulatory, operational, and financial dimensions:
┌─────────────────────────────────────────────────────────────────────────────────────────────┐
│ PASATRU (GARETOSMAB-GRTS) VS SOHONOS (PALOVAROTENE) │
├──────────────────────┬──────────────────────────────────┬───────────────────────────────────┤
│ Dimension │ Pasatru (garetosmab-grts) │ Sohonos (palovarotene) │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Sponsor │ Regeneron Pharmaceuticals │ Ipsen │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ FDA Approval Date │ August 19, 2026 │ August 16, 2023 │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Therapeutic Class │ Fully human monoclonal antibody │ Retinoic acid receptor gamma │
│ & Target │ against Activin A │ (RARγ) selective agonist │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Approved Population │ Adults (aged 18 years and older) │ Females aged 8+; Males aged 10+ │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Indication Scope │ Reduce formation of new HO │ Reduce volume of new heterotopic │
│ │ lesions & clinician flare-ups │ ossification in adults & children │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Route & Dosing │ Monthly IV infusion (60 minutes) │ Daily oral capsule (chronic) with │
│ │ 10 mg/kg (reducible to 3 mg/kg) │ flare-up dose escalation │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Annual List (WAC) │ ~$1.4M average ($693K–$2.1M) │ ~$624,000 baseline (5 mg/day) │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Boxed Warning │ None (fetal harm, skin/soft │ Dual Boxed Warning: Embryo-fetal │
│ │ tissue infection warnings) │ toxicity & epiphyseal closure │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Primary Benefit │ Medical Benefit (Buy-and-Bill, │ Pharmacy Benefit │
│ Channel │ Specialty Infusion, Home IV) │ (Specialty Pharmacy; label-based │
│ │ │ pregnancy prevention, no REMS) │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ HCPCS Coding │ Miscellaneous / Unclassified J │ N/A (Standard NDC retail billing) │
│ Status │ (J3590 / C9399) pending Q-cycle │ │
└──────────────────────┴──────────────────────────────────┴───────────────────────────────────┘
What did FDA approve: Label scope, mechanism, and pediatric boundaries
The primary molecular driver of FOP is a gain-of-function mutation in the ACVR1 (activin A receptor type 1 / ALK2) gene, present in more than 95% of patients (most commonly the R206H mutation). This mutation causes the ACVR1 receptor to aberrantly transduce bone-morphogenetic protein (BMP) signaling in response to Activin A—a ligand that normally acts as an antagonist or weak agonist of wild-type ACVR1.
1. Mechanism of Action: Ligand Neutralization vs Nuclear Receptor Agonism
- Pasatru (garetosmab-grts) is a recombinant fully human IgG4 monoclonal antibody that directly binds and neutralizes Activin A, preventing it from activating the mutant ACVR1/ALK2 receptor complex and thereby blocking the downstream SMAD1/5/8 phosphorylation cascade that initiates heterotopic chondrogenesis and osteogenesis.
- Sohonos (palovarotene) operates downstream through nuclear retinoic acid receptor gamma (RARγ) agonism, inhibiting the differentiation of mesenchymal stem cells into chondrocytes and promoting the degradation of pro-osteogenic signaling intermediates.
2. Label Scope Differences: Lesion Counts vs Volume Metrics
The FDA-approved indication for Pasatru covers two clinical outcomes:
- Reduction in the formation of new heterotopic ossification (HO) lesions — the trial's primary efficacy endpoint; and
- Reduction in clinician-assessed flare-up episodes — a key secondary endpoint that nonetheless made it into the indication statement.
In contrast, Sohonos was licensed to reduce the volume of new heterotopic ossification, assessed by annualized whole-body computed tomography (WBCT, excluding the head).
For payer medical review criteria, Pasatru's endpoint framework provides a more discrete, binary counting metric (presence or absence of new distinct anatomical lesions on imaging) compared to volumetric voxel calculations that require specialized central radiological core-lab measurement.
3. The Pediatric Age Boundary
The most critical clinical and market distinction between the two agents is patient age:
- Pasatru is approved strictly for adults aged 18 and older. Regeneron has planned a pediatric development program (OPTIMA 2) to evaluate younger cohorts, but trial initiation and regulatory expansion remain several years away.
- Sohonos is approved for pediatric patients (females 8 years of age and older; males 10 years of age and older).
Because classical FOP typically manifests in early childhood—with initial flare-ups and permanent heterotopic bone formation frequently occurring before age 10—Sohonos retains a commercial and clinical monopoly in pediatric FOP.
The clinical evidence in payer terms: OPTIMA Phase 3 results
The pivotal evidence supporting Pasatru's Biologics License Application (BLA) was generated in the OPTIMA Phase 3 trial (NCT05394116), a randomized, double-blind, placebo-controlled study enrolling 63 adult patients with FOP across international specialized centers.
┌─────────────────────────────────────────────────────────────────────────────────────────────┐
│ OPTIMA PHASE 3 TRIAL EFFICACY SUMMARY (WEEK 56) │
├────────────────────────────┬──────────────────┬──────────────────────┬──────────────────────┤
│ Study Arm │ Treated (n) │ Mean New HO Lesions │ Lesion Reduction (%) │
├────────────────────────────┼──────────────────┼──────────────────────┼──────────────────────┤
│ Garetosmab 3 mg/kg IV q4w │ n = 19 │ 1 total lesion │ 94% reduction │
│ │ │ (mean 0.05/patient) │ (P = .027) │
├────────────────────────────┼──────────────────┼──────────────────────┼──────────────────────┤
│ Garetosmab 10 mg/kg IV q4w │ n = 23 │ 2 total lesions │ 90% reduction │
│ │ │ (mean 0.09/patient) │ (P = .026) │
├────────────────────────────┼──────────────────┼──────────────────────┼──────────────────────┤
│ Placebo Control │ n = 21 │ 19 total lesions │ Reference Baseline │
│ │ │ (mean 0.90/patient) │ │
└────────────────────────────┴──────────────────┴──────────────────────┴──────────────────────┘
56-WEEK NEW HETEROTOPIC OSSIFICATION LESIONS (OPTIMA TRIAL)
20 ┌──────────────────────────────────────────────────────────┐
│ ██ │ Placebo: 19 lesions
15 │ ██ │ (n=21)
│ ██ │
10 │ ██ │
│ ██ │
5 │ ██ │
│ ░░ ██ │ Garetosmab 10 mg/kg: 2 (n=23)
0 └──────────────────▓▓─────────────────────────────────██───┘ Garetosmab 3 mg/kg: 1 (n=19)
Garetosmab 3mg Garetosmab 10mg Placebo
1. Robust Suppression of Heterotopic Bone Formation
Across the 56-week double-blind period, patients receiving garetosmab experienced near-total suppression of new bone formation:
- In the 3 mg/kg IV arm (n=19), only 1 new HO lesion developed across the entire cohort (a 94% reduction compared to placebo, P = .027).
- In the 10 mg/kg IV arm (n=23), only 2 new HO lesions developed across the entire cohort (a 90% reduction compared to placebo, P = .026).
- In the placebo arm (n=21), patients developed a cumulative total of 19 new HO lesions.
2. Reduction in Acute Flare-Up Activity
In addition to radiographic lesion counts, patients treated with garetosmab demonstrated significant reductions in the frequency and severity of clinician-assessed flare-ups. Given that acute flare-ups cause severe pain, swelling, and systemic inflammation and are frequently the precursors to permanent bone deposition, flare-up suppression serves as a major quality-of-life and functional endpoint.
Safety profile and warning structures: Why Pasatru avoided a boxed warning
The safety evaluation of therapies in FOP requires close examination of both mechanism-related toxicities and clinical trial history.
┌─────────────────────────────────────────────────────────────────────────────────────────────┐
│ SAFETY AND WARNING STRUCTURE COMPARISON │
├─────────────────────────────┬───────────────────────────────┬───────────────────────────────┤
│ Safety Domain │ Pasatru (garetosmab-grts) │ Sohonos (palovarotene) │
├─────────────────────────────┼───────────────────────────────┼───────────────────────────────┤
│ Boxed Warning │ None │ 1. Embryo-Fetal Toxicity │
│ │ │ 2. Premature Epiphyseal │
│ │ │ Closure in growing children│
├─────────────────────────────┼───────────────────────────────┼───────────────────────────────┤
│ Warnings & Precautions │ • Embryo-Fetal Toxicity │ • Mucocutaneous Adverse Rxns │
│ │ • Skin/Soft Tissue Infections │ • Metabolic Bone Loss │
│ │ • Epistaxis & Mucosal Bleed │ • Psychiatric Symptoms │
│ │ • Infusion-Related Reactions │ • Night Blindness / Retinoid │
├─────────────────────────────┼───────────────────────────────┼───────────────────────────────┤
│ Monitoring Requirements │ Pregnancy testing; clinical │ Monthly pregnancy tests; │
│ │ skin exams; infusion monitor │ baseline & periodic linear │
│ │ │ growth / epiphyseal X-rays │
└─────────────────────────────┴───────────────────────────────┴───────────────────────────────┘
1. The Retinoid Toxicity Burden of Sohonos
Sohonos carries a severe safety burden defined by two prominent boxed warnings:
- Embryo-Fetal Toxicity: As a potent systemic retinoid, palovarotene causes major congenital malformations and requires strict label-based pregnancy prevention — pregnancy testing within one week before starting therapy and periodically thereafter, plus contraception starting one month before treatment, during treatment, and for one month after. (Sohonos has no formal REMS; these are label conditions paired with a Medication Guide.)
- Premature Epiphyseal Closure: In growing pediatric patients, palovarotene accelerates the premature fusion of growth plates, resulting in permanent short stature, trunk shortening, and limb length discrepancies. Clinicians must conduct regular radiographic assessments to monitor linear growth.
In addition, most palovarotene-treated patients in the clinical program experienced classic mucocutaneous retinoid side effects, including severe dry skin, cheilitis, alopecia, erythema, and pruritus.
2. Pasatru Safety Profile: Infections, Epistaxis, and Phase 2 History
Pasatru's label does not contain a boxed warning, but carries important Section 5 Warnings and Precautions:
- Embryo-Fetal Toxicity: Activin A plays a critical role in reproductive physiology and embryonic development; effective contraception is mandatory during treatment and for several months post-discontinuation.
- Skin and Soft Tissue Infections: Inhibition of Activin A can alter epithelial tissue repair and local inflammatory defense. In clinical trials, an increased incidence of folliculitis, cellulitis, and superficial skin infections was observed, requiring prompt antibiotic management.
- Epistaxis and Mucosal Bleeding: Mild-to-moderate epistaxis was reported across garetosmab arms, linked to vascular and mucosal signaling alterations.
3. Parsing the Phase 2 LUMINA-1 Safety Signals
P&T committees reviewing Pasatru will note the earlier history of the garetosmab development program. In October 2020, during the open-label extension of the Phase 2 LUMINA-1 trial, Regeneron paused dosing after reports of fatal serious adverse events, and the program was placed on clinical hold; five patient deaths in total were recorded across the open-label periods by the trial's October 2021 database lock (published in the phase 2 trial report, Nature Medicine, 2023).
The published account of those events matters for benefit-risk review. The deaths occurred in patients with severe, advanced baseline FOP, from causes including head and brain trauma due to falls in the setting of severe motor disability, hemorrhagic stroke, intestinal obstruction, traumatic spleen rupture with cardiac arrest after a fall, and sudden cardiac death. Investigators reported the deaths as unrelated to garetosmab and the authors concluded a definitive causal link was not established, while acknowledging a causal relationship could not be excluded. LUMINA-1 was subsequently closed, and Regeneron designed the Phase 3 OPTIMA trial as a fresh protocol with structured monitoring and a dose-reduction option (10 mg/kg starting dose, reducible to 3 mg/kg for tolerability).
Launch economics and pricing: What $1.4M WAC means next to $624K
Pasatru launches with an average annual Wholesale Acquisition Cost (WAC) of approximately $1.4 million for an adult patient of average weight receiving the standard 10 mg/kg monthly regimen. Because dosing is weight-based (supplied in 300 mg/5 mL single-dose vials), annual drug costs scale with body weight and dose tier, creating a commercial range from $693,000 (for lower-weight adults or 3 mg/kg maintenance) up to $2.1 million (for higher-weight adults on 10 mg/kg).
┌─────────────────────────────────────────────────────────────────────────────────────────────┐
│ ANNUAL LIST PRICE AND CHANNEL COMPARISON │
├──────────────────────┬──────────────────────────────────┬───────────────────────────────────┤
│ Economic Variable │ Pasatru (garetosmab-grts) │ Sohonos (palovarotene) │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Annual List (WAC) │ ~$1,400,000 average │ ~$624,000 standard maintenance │
│ │ ($693,000 to $2,100,000 range) │ (escalates during active flare) │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Pricing Metric │ Weight-based (10 mg/kg or 3mg/kg)│ Fixed oral dosing (5 mg daily; │
│ │ per 4-week infusion cycle │ up to 20 mg/day during flare-ups) │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Adjudication Pathway │ Medical Benefit (HCPCS billing) │ Pharmacy Benefit (NCPDP claim) │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Administration Costs │ IV infusion chair / home nursing │ None (Self-administered oral) │
│ │ fees, premedication, IV supplies │ │
├──────────────────────┼──────────────────────────────────┼───────────────────────────────────┤
│ Distribution Model │ Limited Distribution Specialty │ Specialty Pharmacy / Hub │
│ │ Infusion Hub (Regeneron myRARE) │ (Ipsen Cares) │
└──────────────────────┴──────────────────────────────────┴───────────────────────────────────┘
Why the Price Premium Exists
Regeneron's pricing strategy reflects three market realities:
- Clinical Superiority on Lesion Counts: OPTIMA demonstrated a 90% to 94% reduction in new HO lesions versus randomized placebo with no boxed warning, compared to Sohonos's 54% reduction in annualized new-HO volume versus an external natural-history cohort in its pivotal MOVE trial (nominal P = .039) — a cross-trial comparison, not head-to-head evidence.
- Adult Population Cap: Because Pasatru is restricted to adults, its addressable patient pool is narrower than Sohonos's label, concentrating fixed development recovery into a smaller prevalent population.
- Biologic Infusion Value Benchmark: The ultra-rare biologic benchmark (e.g., enzyme replacement therapies, complement inhibitors, and rare-disease mAbs) typically ranges from $500,000 to $1.5M+ annually, whereas oral small molecules face lower payer acceptance thresholds.
For broader context on how health plans manage multi-million-dollar ultra-rare therapies, see our analysis of rare-disease launch access.
Channel logistics: Navigating buy-and-bill vs home infusion
Because Pasatru is a monthly 60-minute intravenous infusion, health plans and treating specialists face significant channel-routing decisions.
PASATRU ACCESS & REIMBURSEMENT WORKFLOW
┌────────────────────────────────────────────────────────┐
│ 1. CLINICAL IDENTIFICATION & GENETIC CONFIRMATION │
│ Adult 18+ with documented ACVR1/ALK2 mutation │
└───────────────────────────┬────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────┐
│ 2. BENEFIT INVESTIGATION (Regeneron myRARE) │
│ Route via Medical Benefit vs Specialty Pharmacy │
└───────────────────────────┬────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────┐
│ 3. PRIOR AUTHORIZATION SUBMISSION │
│ Submit baseline WBCT / flare-up history │
└───────────────────────────┬────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────┐
│ 4. SITE-OF-CARE SELECTION │
│ Hospital Outpatient ──► Ambulatory ──► Home IV │
└───────────────────────────┬────────────────────────────┘
│
▼
┌────────────────────────────────────────────────────────┐
│ 5. CLAIMS BILLING & REAUTHORIZATION │
│ Interim J3590/C9399 ──► Reauth at Month 12 on WBCT │
└────────────────────────────────────────────────────────┘
1. Site-of-Care Economics
Patients with FOP often suffer from severe joint ankylosis, spinal fusion, and mobility restrictions that make monthly travel to hospital outpatient infusion centers hazardous. (Minor falls or physical trauma can trigger catastrophic flare-ups).
- Hospital Outpatient Departments (HOPD): Bill a separate facility fee on top of drug acquisition that payers will aggressively seek to redirect toward lower-cost settings.
- Home Infusion Nursing: Pasatru can be administered across a range of care settings, including home infusion where appropriate, per Regeneron — a meaningful option for a population in whom travel itself carries injury risk. Regeneron's myRARE support program (benefits investigation, insurance verification, and financial-support resources for eligible patients) sits alongside the channel decision rather than replacing it.
2. Interim Billing Risk and HCPCS Coding
Because Pasatru is newly approved, it enters the market without a dedicated Healthcare Common Procedure Coding System (HCPCS) J-code. For the first two to three calendar quarters (typically 6 to 9 months), providers must bill using unclassified biologic codes:
- J3590 (Unclassified biologics) for physician-office and home-infusion claims; or
- C9399 (Unclassified drugs and biologicals) for hospital outpatient claims under OPPS.
Unclassified billing creates high administrative friction, requiring manual claim attachment of the National Drug Code (NDC), invoice pricing, dosage calculations, and FDA approval documentation. Providers who lack experience with ultra-rare buy-and-bill inventory may refuse to purchase $100,000+ monthly vials on speculation, driving claims toward specialty pharmacy "white bagging" where the specialty pharmacy dispenses the drug directly to the infusion provider.
For detailed operational guidance on managing unclassified claims, see our guide on interim billing risk for newly launched biologics.
Payer coverage criteria: Building the Prior Authorization file
Commercial and Medicaid health plans will rapidly establish formal Prior Authorization (PA) and utilization management policies for Pasatru. Access teams should expect criteria heavily modeled on existing ultra-rare rare-bone disease policies.
┌─────────────────────────────────────────────────────────────────────────────────────────────┐
│ TYPICAL PASATRU PRIOR AUTHORIZATION CRITERIA │
├─────────────────────────┬───────────────────────────────────────────────────────────────────┤
│ Criterion │ Documentation Required for Initial Approval (12 Months) │
├─────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ Age Requirement │ Patient must be 18 years of age or older at treatment initiation. │
├─────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ Genetic Confirmation │ Confirmed heterozygous mutation in the ACVR1/ALK2 gene │
│ │ (e.g., c.617G>A, p.R206H or documented pathogenic variant). │
├─────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ Baseline Disease │ Documented baseline Whole-Body CT (WBCT) or low-dose CT scan │
│ Documentation │ establishing current heterotopic ossification burden. │
├─────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ Prescriber Specialty │ Prescribed by or in consultation with a medical geneticist, │
│ │ endocrinologist, or bone disease specialist with FOP expertise. │
├─────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ Concomitant Therapy │ Cannot be used in combination with palovarotene (Sohonos) or │
│ Exclusion │ investigational ALK2 inhibitors. │
├─────────────────────────┼───────────────────────────────────────────────────────────────────┤
│ Reauthorization Metric │ At 12 months: Documented stabilization or reduction in the rate │
│ (Renewal at 12 Months) │ of new HO lesion formation compared to pre-treatment baseline. │
└─────────────────────────┴───────────────────────────────────────────────────────────────────┘
The Reauthorization Trap: Proving Stability vs Improvement
In degenerative rare diseases, the greatest coverage friction occurs at renewal. As documented in our review of Sohonos prior authorization criteria in FOP, payers often draft rigid renewal criteria requiring "documented objective clinical improvement."
Because neither Pasatru nor Sohonos can dissolve or reverse pre-existing heterotopic bone, the therapeutic goal is prevention of new bone lesions and flare-up mitigation. Market-access teams must work with medical directors to ensure renewal language explicitly defines absence of new HO lesions or reduction in flare-up frequency as meeting renewal criteria.
Furthermore, launch products frequently face administrative 180-day new-to-market review blocks while P&T committees review dossiers. Teams should consult our framework on payer blocks in the first 180 days to navigate exception requests and single-case agreements.
Competitive outlook: Sohonos, Pasatru, and the pipeline
The FOP landscape is transitioning from zero approved therapies prior to 2023 into a multi-product competitive market.
FOP TREATMENT LANDSCAPE TIMELINE & PIPELINE
2023 ───► FDA Approves SOHONOS (Ipsen)
• Oral RARγ agonist (Ages 8+ F / 10+ M)
• Dual Boxed Warning (Teratogenicity & Epiphyseal Closure)
• $624K Annual WAC
2026 ───► FDA Approves PASATRU (Regeneron)
• IV Activin A mAb (Adults 18+)
• No Boxed Warning; 90-94% Lesion Reduction
• ~$1.4M Annual WAC
SEPT ───► PDUFA DATE: ZILURGISERTIB (Mirum / Incyte)
2026 • Oral selective ALK2 kinase inhibitor
• Pivotal PROGRESS Phase 2 (Ages 12+)
• Potential first oral targeted kinase inhibitor
1. Switching Dynamics in Adult Patients
In adult FOP patients currently stabilized on Sohonos, prescribers and patients will evaluate switching to Pasatru based on:
- Tolerability: Eliminating chronic mucocutaneous retinoid side effects (dry skin, cheilitis, skin peeling) in favor of monthly IV infusions.
- Efficacy: Seeking stronger suppression of new lesions based on OPTIMA's 90–94% lesion reduction.
- Administration Burden: Weighing a monthly 60-minute infusion against daily oral capsules.
2. The Next Wave: Mirum's Zilurgisertib
Mirum Pharmaceuticals (which licensed worldwide rights to the asset from Incyte in 2026) has filed zilurgisertib (INCB000928), an investigational oral selective small-molecule inhibitor of ALK2 kinase activity studied in the pivotal Phase 2 PROGRESS trial in patients aged 12 and older; the NDA is under FDA priority review with an action date of September 26, 2026. If approved, zilurgisertib would offer targeted intracellular ALK2 kinase inhibition via an oral route, intensifying three-way competition across mechanisms (ligand neutralization vs kinase inhibition vs nuclear RARγ agonism).
Frequently Asked Questions
Is Pasatru approved for children with FOP?
No. The FDA approval of Pasatru is restricted to adults aged 18 years and older. Regeneron plans to conduct a pediatric clinical trial (OPTIMA 2), but until pediatric data are submitted and approved, Sohonos (palovarotene) remains the only FDA-approved option for pediatric patients (females 8+ and males 10+).
Does Pasatru have an FDA boxed warning?
No. Unlike Sohonos, which carries a dual boxed warning for embryo-fetal toxicity and premature epiphyseal closure in growing children, Pasatru does not carry a boxed warning. Its label includes Section 5 Warnings and Precautions for embryo-fetal toxicity, skin and soft-tissue infections, and epistaxis.
Can Pasatru be administered as a home infusion?
Yes. Regeneron states Pasatru can be administered across a range of care settings, including home infusion where appropriate, using its 60-minute monthly infusion protocol delivered by trained specialty nurses — which minimizes travel-associated physical trauma for patients with severe mobility impairment. The company's myRARE program separately provides benefit verification and financial-support resources.
Why did garetosmab's Phase 2 program raise safety questions?
During the open-label extension of the Phase 2 LUMINA-1 trial, dosing was paused in October 2020 after fatal serious adverse events; five deaths in total were recorded across the open-label periods by the 2021 database lock. The published trial report attributed the deaths to causes common in advanced FOP — falls with head trauma, stroke, intestinal obstruction, and sudden cardiac death — and found no established causal link to garetosmab, while noting a causal relationship could not be excluded. LUMINA-1 was closed and the Phase 3 OPTIMA trial ran under a new protocol with enhanced monitoring.
What HCPCS code applies to Pasatru at launch?
At launch, Pasatru does not have a permanent J-code. Providers must bill using miscellaneous HCPCS codes J3590 (unclassified biologic) or C9399 (unclassified drug/biologic under OPPS) accompanied by the specific 11-digit NDC, invoice cost, and clinical documentation until CMS assigns a permanent Q- or J-code.
Sources
- U.S. Food and Drug Administration (FDA): FDA Approves Second Treatment for Fibrodysplasia Ossificans Progressiva (Pasatru). FDA News Release, August 19, 2026. fda.gov.
- Regeneron Pharmaceuticals: Pasatru™ (garetosmab-grts) Approved by FDA as Treatment for Fibrodysplasia Ossificans Progressiva (FOP). Investor News Release, August 19, 2026. investor.regeneron.com.
- ClinicalTrials.gov: Study to Evaluate the Efficacy and Safety of Garetosmab in Patients With Fibrodysplasia Ossificans Progressiva (OPTIMA). Identifier: NCT05394116. Updated July 17, 2026. clinicaltrials.gov.
- Di Rocco C, Forleo-Neto H, Pignolo RJ, et al. (Nature Medicine, 2023): Garetosmab in fibrodysplasia ossificans progressiva: a randomized, double-blind, placebo-controlled phase 2 trial (includes the open-label-period deaths and safety review). PMC10579054. pmc.ncbi.nlm.nih.gov.
- Managed Healthcare Executive: FDA Approves Pasatru, the Second Treatment for Rare Bone Disorder. August 20, 2026. managedhealthcareexecutive.com.
- U.S. Food and Drug Administration (FDA): FDA Approves First Treatment for Fibrodysplasia Ossificans Progressiva (Sohonos). August 16, 2023. fda.gov.
- Ipsen Biopharmaceuticals: US FDA Approves Ipsen's Sohonos™ (palovarotene) Capsules. August 16, 2023. ipsen.com.
- Pignolo RJ, et al. (Orphanet Journal of Rare Diseases, 2021): IFOPA-commissioned US FOP prevalence study (adjusted US prevalence 0.88 per million). PMC.
