Why Is Insmed Stock Falling Thursday?

by | Dec 18, 2025 | General

Insmed Incorporated (NASDAQ:INSM) stock plunged on Thursday.

• Insmed stock is showing notable weakness. What’s behind INSM decline?

The company released data from the Phase 2b BiRCh study of brensocatib in patients with chronic rhinosinusitis without nasal polyps (CRSsNP).

The trial did not meet its primary or secondary efficacy endpoints in either the 10 mg or 40 mg treatment arms.

Brensocatib was well tolerated, with no new safety signals identified, including in the 40 mg arm, which is the highest dose Insmed has studied to date.

Insmed has discontinued its development program of brensocatib in CRSsNP, effective immediately, and intends to present these data at a future congress.

Also Read: Lung Disease-Focused Insmed ‘Must-Own’ Name For Investors

“Given that there are no animal models in this disease, the purpose of this proof-of-concept study was to determine if brensocatib could provide treatment benefit to patients with CRSsNP,” said Insmed Medical Officer Martina Flammer, M.D., MBA.

In the study, a negative score in the primary endpoint of change from baseline to the 28-day average of daily Sinus Total Symptom Score (sTSS) at Week 24 indicated an improvement.

Topline results from each treatment arm were as follows: placebo least squares (LS) mean was -2.44; brensocatib 10 mg LS mean was -2.21; and brensocatib 40 mg LS mean was -2.33.

In August, the U.S. Food and Drug Administration (FDA) approved Brinsupri (brensocatib 10 mg and 25 mg tablets).

It is an oral, once-daily treatment for non-cystic fibrosis bronchiectasis (NCFB) in adults and children 12 years and older.

Acquisition of Phase 2 Ready Asset

Insmed also acquired INS1148, an investigational monoclonal antibody to address respiratory and immunological and inflammatory diseases.

Insmed plans to advance Phase 2 development programs for INS1148 initially in interstitial lung disease and moderate-to-severe asthma. Opsidio, a private, clinical-stage company, developed INS1148 (formerly known as OpSCF).

Analyst Take

“While the BiRCh study always carried some clinical risk given the lack of previous data with DPP1 inhibition in CRSsNP and lack of numerous clinical datasets to understand potential placebo response rates,” William Blair wrote on Thursday.

However, even without the CRSsNP opportunity, analyst Matt Phipps said that Brinsupri will continue to have a strong launch in bronchiectasis, and that the company’s other lead programs (Arikayce and TPIP) also have meaningful expansion opportunities.

The analyst reiterates the Outperform rating.

RBC Capital maintains Insmed with an Outperform and lowers the price target from $215 to $195.

Guggenheim maintains a Buy rating, lowering the price target from $230 to $221.

ISMN Action: INSM stock is down 15.28% at $168.14 at publication on Thursday.

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