Approval brief · Health
The approval counts new bone without claiming old bone disappears
Read the OPTIMA result through four separate questions about disease activity, dose, function and safety.
- The endpoint was new heterotopic boneFull-body low-dose CT found 19 new lesions with placebo, one with 3 mg/kg and two with 10 mg/kg by Week 56.
- The FDA claim also includes clinician-assessed flare-upsAdults received an infusion every four weeks, and both lesion formation and episodes of pain, swelling or worsening were evaluated.
- The approved starting dose is 10 mg/kgThe label allows a decrease to 3 mg/kg every four weeks when the starting dose is not tolerated.
- Prevention is not reversalThe approval does not say existing heterotopic bone dissolves, lost movement returns or the adult result automatically applies to children.
On 19 August 2026, the FDA approved Pasatru, or garetosmab-grts, for adults with fibrodysplasia ossificans progressiva. The indication is to reduce new heterotopic ossification and clinician-assessed disease flare-ups. It is the second U.S.-approved treatment for this ultra-rare disease and the first approved antibody directed at the Activin A pathway that drives abnormal bone formation in FOP.
The useful reading is narrower than “the disease has been stopped.” OPTIMA measured new lesions forming during a 56-week randomized period. That endpoint can establish less new bone growth without proving that bone already present has disappeared or that a fixed joint has regained function.
The claim follows disease activity forward
Pasatru is approved for adults to reduce new heterotopic ossification and clinician-assessed flare-ups. The wording is prospective: it addresses additional disease activity after treatment begins rather than undoing the accumulated skeletal burden.
FOP makes a normal repair signal build bone in the wrong tissue
FOP is caused by pathogenic variation in ACVR1, which encodes activin A receptor type 1. In the altered receptor, Activin A can trigger signaling that promotes bone formation where bone should not exist. Muscles, tendons, ligaments and other connective tissues can progressively ossify, restricting movement and creating cumulative disability.
Garetosmab is a monoclonal antibody that neutralizes Activin A. The mechanism is therefore upstream of the lesion count: reduce the signal that activates abnormal bone formation, then test whether fewer new lesions appear on imaging. Mechanism explains why the trial was plausible; the randomized endpoint tests whether the expected biological effect occurred.
OPTIMA turned the disease into a countable 56-week endpoint
The phase 3 OPTIMA study randomized 63 adults to placebo, garetosmab 3 mg/kg or garetosmab 10 mg/kg by intravenous infusion every four weeks. Full-body low-dose CT was used to detect new heterotopic ossification lesions through Week 56. Twenty-one adults received placebo, 19 received 3 mg/kg and 23 received 10 mg/kg.
The Lesion Ledger keeps four claims in separate columns
The approval becomes easier to interpret when accumulated disease, new disease activity, clinical flare-ups and function are not compressed into one result. Each belongs to a different evidentiary account.
Record what already exists before crediting what treatment prevented
The four accounts move in one direction but cannot be substituted for one another.
Accumulated lesions and fixed limitations are present before the randomized clock begins.
OPTIMA tests how much additional anatomical disease appears by Week 56.
Pain, swelling or worsening adds a clinician-assessed activity measure.
Longer follow-up must show how prevention changes mobility and daily life.
The dose result is not a simple more-is-better ladder
Both study doses sharply reduced new lesions. The 3 mg/kg group had one new lesion and 53 clinician-assessed flare-ups; the 10 mg/kg group had two new lesions and nine flare-ups; placebo had 19 lesions and 66 flare-ups. The lesion counts are small absolute numbers, while the flare-up pattern favors the higher dose more clearly.
10 mg/kg by IV infusion every four weeks
The FDA-selected starting dose aligns the lesion result with the markedly lower clinician-assessed flare-up count observed in OPTIMA.
Decrease to 3 mg/kg when needed
The lower dose remains an approved fallback if 10 mg/kg is not tolerated; this is a clinical dose decision, not a self-directed adjustment.
Safety and population limits remain part of the approval
The FDA information warns about fetal harm, skin and soft-tissue infections that can require treatment or hospitalization, and nosebleeds requiring medical intervention. Common adverse reactions include nosebleeds, increased hair growth, abscess and acne. People who can become pregnant are advised to use effective contraception during treatment and for six months after the last dose.
OPTIMA enrolled adults. A separate phase 3 study is designed to investigate garetosmab in children and adolescents, with its own safety, pharmacokinetic and efficacy questions. An adult approval should not be translated into a pediatric conclusion before those data exist.
Whether lesion suppression remains stable during longer exposure.
How preventing new bone changes mobility, independence and respiratory burden over years.
Whether benefit, dose and risk translate to growing children and adolescents.
Questions about garetosmab and FOP
What is garetosmab approved to do?
Pasatru is approved for adults with FOP to reduce new heterotopic ossification and clinician-assessed disease flare-ups.
Does garetosmab remove bone that already formed?
The FDA approval is based on reducing new lesions and flare-ups. It does not claim reversal of existing heterotopic bone.
How was new bone measured in OPTIMA?
The primary endpoint counted new heterotopic ossification lesions detected by full-body low-dose CT through Week 56.
Is garetosmab approved for children with FOP?
No. The August 2026 approval covers adults. A separate pediatric phase 3 study is listed by ClinicalTrials.gov.
