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Diseases

Regeneron Races to Regulators with Phase 3 Win in Ultrarare Disease

Strategic Insights

— 1 min read

Regeneron is quickly moving forward with FDA approval plans for its treatment garetosmab in fibrodysplasia ossificans progressiva (FOP) after a phase 3 clinical trial demonstrated a significant reduction in abnormal bone lesions. The study, which enrolled 63 adults with FOP, randomized patients to receive one of two doses of garetosmab or placebo for 56 weeks. The results showed a 90% or greater reduction in lesions in both treatment arms, meeting the primary endpoint. While a key secondary endpoint of clinician-assessed flare-ups was not statistically significant at the low dose, the high dose showed a 89% reduction compared to placebo, a statistically significant result.

Key Takeaways:

  • The phase 3 clinical trial enrolled 63 adults with FOP and randomized patients to receive one of two doses of garetosmab or placebo for 56 weeks.
  • The study met its primary endpoint with a 90% or greater reduction in lesions in both treatment arms.
  • The high dose of garetosmab showed a 89% reduction in clinician-assessed flare-ups compared to placebo, a statistically significant result.
  • Related, Ipsen's Sohonos, approved for FOP in 2023, has underperformed commercially, with sales decreasing 20% to 8.3 million euros in the first half of 2025.
  • Regeneron is planning to start a phase 3 trial in adolescents and children with FOP next year.

Statistics:

  • 63 adults with FOP were enrolled in the phase 3 clinical trial.
  • The study showed a 90% or greater reduction in lesions in both treatment arms.
  • The high dose of garetosmab showed a 89% reduction in clinician-assessed flare-ups compared to placebo.
  • 20% of Regeneron's researchers believed that the deaths in the phase 2 trial of garetosmab were unlikely to be related to the treatment.
  • 44 patients were enrolled in the extension part of the phase 2 trial, 5 of whom died.
  • $330 million is the estimated impairment loss related to Sohonos sales.

Sources:

  • Regeneron press release, dated 2023-02-01, announcing the phase 3 clinical trial results.
  • Regeneron Scientific Data, dated 2020-08-01, describing the phase 2 clinical trial results.
  • Ipsen company report, dated 2025-01-31, reporting impairment loss related to Sohonos sales.

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