A new gMG agent must address FcRn-inadequate responders or claim a serostatus niche efgartigimod's dominance has left open.

Efgartigimod (Vyvgart/Vyvgart Hytrulo) holds roughly 50% of the US refractory generalised MG market and has set both the clinical and pricing bar the rest of the class is measured against. Rozanolixizumab (Rystiggo), the second FcRn antagonist, has gained limited traction against argenx's KOL loyalty; zilucoplan (Zilbrysq), a self-injected anti-C5 agent, is building a separate lower-cost niche in AChR+ patients. A new entrant competes against an estimated 1,200-2,100 US patients, 30-35% of the 4,000-6,000 on FcRn therapy, who remain inadequately controlled despite treatment, patients whose disease appears to involve non-IgG mechanisms that IgG-reduction alone does not resolve.

Serostatus segmentation is now standard in US gMG clinical thinking: AChR-Ab+ patients, roughly 85% of gMG, respond to both FcRn and complement-pathway agents; MuSK-Ab+ patients, roughly 8%, respond poorly to complement inhibitors because MuSK+ disease is IgG4-mediated rather than complement-activating, leaving FcRn as the better but still incomplete option; seronegative patients, roughly 7%, an estimated 490-700 US patients, are the least mechanistically understood and least studied subtype, with no agent purpose-built for them. A drug with MuSK+-specific or seronegative-specific clinical data would claim a genuinely first-in-class commercial position rather than a fourth me-too entrant.

Seronegative gMG patients remain the least studied subtype, with no purpose-built agent.

Five questions this report answers:

Q1 - Should a new gMG agent target FcRn-inadequate responders or a specific serostatus niche?

Q2 - What IST step-edit and PA framework will a new MG agent face at launch?

Q3 - What ICER-anchored value benchmark should a new MG entrant's payer dossier build on?

Q4 - What deliverable formats come with a commissioned US myasthenia gravis launch readiness assessment?

Q5 - Which patient population should a pre-launch myasthenia gravis asset target in the US?

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Mike || Global Pharma Commercial Marketing Head

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