01—Abstract
Summary
Summary of the 8-K filed March 23, 2026. Cited figures are marked; the original filing is the authoritative source.
Insmed Incorporated (Nasdaq: INSM) announced positive topline results from its Phase 3b ENCORE study of ARIKAYCE (amikacin liposome inhalation suspension) plus multidrug therapy (azithromycin 250 mg + ethambutol 15 mg/kg) once daily versus placebo plus multidrug therapy in diagnosed patients with a new occurrence of Mycobacterium avium complex (MAC) lung infection who had not received antibiotics.
The study randomized 425 patients 1:1 (213 ARIKAYCE, 212 placebo) across 177 sites globally. The primary endpoint, change from baseline in Respiratory Symptom Score at Month 13, was 17.77 points for ARIKAYCE versus 14.66 points for placebo, a treatment difference of 3.11 points (p=0.0299, statistically significant). All multiplicity-controlled secondary culture conversion endpoints were statistically significant (p<0.0001), including culture conversion by Month 6 (87.8%a vs. 57.0%) and durable culture conversion at Month 15 (76.2% vs. 47.6%).
The PROMIS Fatigue T-score change at Month 13 was not statistically significant (p=0.2900). The company states it has completed the study intended to fulfill the FDA post-marketing requirement. Insmed plans to file a supplemental new drug application (sNDA) for ARIKAYCE in MAC lung disease in the second half of 2026 to seek label expansion and traditional approval for the existing refractory indication in the U.S., and to submit data to Japan's PMDA in the same period.
The safety profile was described as consistent with the known profile, with no new safety signals. Dysphonia (58.7%b vs. 8.5%), cough, and dyspnea were more frequent on ARIKAYCE, and bronchospasm (23.0% vs. 11.8%) and hypersensitivity pneumonitis (2.3% vs. 0%) occurred in notably more ARIKAYCE patients. No deaths were considered related to study drug, and the treatment discontinuation rate was 18.3% on ARIKAYCE versus 11.8% on comparator.
The company also furnished a press release (Exhibit 99.1) and a slide presentation (Exhibit 99.2) and hosted a conference call on March 23, 2026 at 8:00 a.m. ET. The filing notes that additional data will be presented at future medical meetings.
02—Key points
Key Highlights
- Primary endpoint met: change in Respiratory Symptom Score at Month 13 was 17.77 points for ARIKAYCE vs. 14.66 points for placebo, a 3.11-point treatment difference (p=0.0299).
- All multiplicity-controlled secondary culture conversion endpoints were statistically significant (p<0.0001): culture conversion by Month 6 at 87.8% vs. 57.0%, and durable culture conversion at Month 15 at 76.2% vs. 47.6%.
- The PROMIS Fatigue T-score change at Month 13 showed a -0.81 treatment difference that was not statistically significant (p=0.2900).
- Exploratory Respiratory Symptom Score change at Month 15 was 16.63 vs. 11.83 points (4.80-point difference, nominal p=0.0015).
- Insmed has completed the study intended to fulfill the FDA post-marketing requirement and plans an sNDA in the second half of 2026 for potential label expansion and traditional approval for the existing U.S. refractory indication.
- Insmed plans to submit the data to Japan's PMDA in the second half of 2026 to support potential label expansion in Japan.
- Safety: no new safety signals; bronchospasm (23.0% vs. 11.8%) and hypersensitivity pneumonitis (2.3% vs. 0%) were notably higher on ARIKAYCE, and dysphonia was 58.7% vs. 8.5%; no deaths were considered related to study drug.
03—Questions
Frequently Asked Questions
What did the ENCORE study test and in which patients?
ENCORE evaluated ARIKAYCE plus multidrug therapy (azithromycin 250 mg and ethambutol 15 mg/kg, once daily) versus placebo plus the same multidrug therapy in 425 adults diagnosed with a new occurrence of MAC lung infection who had not received antibiotics. Patients were randomized 1:1 and treated once daily for 12 months, followed by three months off treatment to assess durability of culture conversion.
Did the study meet its primary endpoint?
Yes. The change from baseline in Respiratory Symptom Score at Month 13 was 17.77 points for ARIKAYCE versus 14.66 points for placebo, a treatment difference of 3.11 points (p=0.0299, statistically significant). The filing notes the Month 13 result was statistically significant.
What regulatory steps does Insmed plan next?
Insmed plans to file a supplemental new drug application with the FDA in the second half of 2026 for potential label expansion in MAC lung disease and to obtain traditional approval for the existing refractory indication in the U.S. It also plans to submit the data to Japan's PMDA in the second half of 2026 to support potential label expansion in Japan.
What were the main safety concerns in the trial?
The company reported no new safety signals. Dysphonia (58.7% vs. 8.5%), cough (32.9% vs. 14.6%), and dyspnea (16.4% vs. 5.7%) were more common on ARIKAYCE. Bronchospasm (23.0% vs. 11.8%) and hypersensitivity pneumonitis (2.3% vs. 0%) occurred in notably more ARIKAYCE patients. Treatment discontinuation was 18.3% on ARIKAYCE vs. 11.8% on comparator, and no deaths were considered related to ARIKAYCE or placebo.
Were all efficacy endpoints statistically significant?
No. The primary endpoint and all multiplicity-controlled secondary culture conversion endpoints were statistically significant. The PROMIS Fatigue T-score change at Month 13 (-0.81 treatment difference, p=0.2900) was not statistically significant. Some exploratory and secondary endpoints, such as the meaningful within-patient change thresholds, had nominal p-values not adjusted for multiplicity control.
04—Continue