Insmed Stock Retreats on Phase 2b BiRCh Setback, Pivots Strategy With Monoclonal Antibody Acquisition

Insmed Inc. (INSM) announced a significant strategic pivot following disappointing Phase 2b trial results. The company has acquired INS1148, a monoclonal antibody candidate at the clinical stage developed by Opsidio. The acquisition terms remained undisclosed, though Insmed plans to advance the asset into Phase 2 trials targeting interstitial lung disease and moderate-to-severe asthma—a shift that underscores management’s effort to offset recent clinical setbacks.

Failed Phase 2b Study Triggers Sharp Market Correction

The BiRCh Phase 2b study evaluating brensocatib for chronic rhinosinusitis without nasal polyps (CRSsNP) failed to achieve either its primary or secondary efficacy endpoints across both the 10 mg and 40 mg dosing regimens. Insmed has decided to immediately halt its brensocatib development program in CRSsNP. The news triggered an immediate market reaction, with INSM shares declining 21.39% in after-hours trading following the disclosure.

Over the preceding 12 months, INSM had traded between $60.40 and $212.75, reflecting significant volatility typical of biopharmaceutical stocks dependent on clinical trial outcomes. Prior to the announcement, the stock closed at $198.46, already down 1.10% during regular trading.

Recalibrating the Portfolio

Martina Flammer, M.D., MBA, Chief Medical Officer of Insmed, acknowledged the disappointment but emphasized the clarity gained: “While we are disappointed in the results, they provided us with a clear answer. We extend our sincerest gratitude to the patients and investigators who made the BiRCh study possible.”

The acquisition of INS1148 represents an attempt to redirect development resources toward conditions with potentially larger market opportunities and clearer clinical pathways. By entering Phase 2 with a monoclonal antibody in respiratory and inflammatory indications, Insmed aims to rebuild investor confidence following the brensocatib setback.