December 18, 2025 — Insmed Incorporated (NASDAQ: INSM) shares dropped sharply Thursday after the company disclosed a Phase 2b setback for brensocatib in a chronic sinus condition and said it is discontinuing development in that indication, even as it simultaneously added a new Phase 2–ready antibody to its pipeline. [1]
Insmed stock was trading around $166.75 in the afternoon snapshot available from market data, down about 16% on the day, after touching an intraday low of $158.06 and high of $173.99.
What happened to INSM stock on December 18, 2025
The selloff traces back to Insmed’s disclosure that its Phase 2b BiRCh trial of brensocatib in chronic rhinosinusitis without nasal polyps (CRSsNP) missed both its primary and secondary endpoints, prompting the company to end the CRSsNP program. [2]
Brensocatib is marketed as BRINSUPRI for non-cystic fibrosis bronchiectasis (NCFB), and investors had been watching whether the drug could expand into additional inflammatory conditions—an effort that took a hit with Thursday’s trial outcome. [3]
The BiRCh data: placebo matched or beat brensocatib on symptoms
In the BiRCh study, 288 patients were randomized 1:1:1 to receive brensocatib 10 mg, brensocatib 40 mg, or placebo for 24 weeks, on top of mometasone furoate nasal spray as background therapy. The primary endpoint was the change from baseline in the 28‑day average daily Sinus Total Symptom Score (sTSS) at Week 24. [4]
According to Insmed’s disclosure, results for the primary endpoint were:
- Placebo LS mean:-2.44
- Brensocatib 10 mg LS mean:-2.21
- Brensocatib 40 mg LS mean:-2.33 [5]
In other words, the drug did not separate from placebo in a way that supported continued development in CRSsNP—an outcome some analysts characterized as a “worst-case” readout because it offered little guidance for pursuing subgroups or alternative trial designs. [6]
Safety was consistent, but Insmed is still stopping the CRSsNP program
One notable detail: Insmed reported brensocatib was well tolerated, with no new safety signals identified—even at 40 mg, the highest dose the company has studied to date in this setting. [7]
The company also disclosed treatment-emergent adverse event (TEAE) rates that were broadly comparable across arms (for example, “any TEAE” was reported at 63.6% in the 10 mg arm, 69.9% in the 40 mg arm, and 65.3% on placebo). [8]
Despite the clean-ish safety profile, Insmed said it has discontinued development of brensocatib in CRSsNP and intends to present the full dataset at a future scientific meeting. [9]
Why the market reacted so strongly
From a stock narrative perspective, CRSsNP mattered because it was viewed as a potentially large expansion opportunity for brensocatib beyond NCFB. Barron’s reported that some investors had been pricing in hundreds of millions to $1 billion in potential peak sales tied to that expansion thesis—expectations that were abruptly repriced after the miss. [10]
BioPharma Dive framed the moment as a break in Insmed’s recent “win streak,” noting the company’s valuation had surged earlier in 2025 as positive clinical and commercial momentum accumulated—meaning the bar for “no news” was already higher than usual. [11]
Insmed’s pipeline counterpunch: the INS1148 acquisition
Alongside the BiRCh update, Insmed announced it has acquired INS1148 (previously known as OpSCF), described as a Phase 2–ready monoclonal antibody with potential applications across respiratory and immunological/inflammatory diseases. [12]
Insmed says INS1148 is designed to preferentially target the SCF248 isoform of stem cell factor, aiming to block inflammatory signaling downstream of c‑Kit while preserving key “homeostatic and tissue healing” pathways. The company plans to initially advance INS1148 into Phase 2 programs in interstitial lung disease (ILD) and moderate-to-severe asthma. [13]
Insmed did not disclose deal terms in its public statement or the related 8‑K disclosure. [14]
That said, BioPharma Dive reported that analysts believed Insmed paid $40 million upfront, with potential royalties and milestone payments to the seller, Opsidio (those figures were attributed to analyst commentary rather than a company-confirmed price). [15]
Fierce Pharma also noted that Opsidio had been developing the antibody for chronic inflammation and that the program had been developed in partnership with AbbVie, with Opsidio running a Phase 2a study in moderate-to-severe atopic dermatitis—context that helps explain why Insmed framed INS1148 as “Phase 2 ready.” [16]
Analyst forecasts on December 18: price targets fall, but many ratings hold
In a biotech stock, “the data” is only half the story—the other half is what the Street believed the data would look like. On Dec. 18, multiple analysts moved quickly to revise models and targets while largely keeping bullish ratings intact.
Here are some of the widely reported target changes and stances published today:
- RBC Capital Markets: cut target to $195 from $215, maintained Outperform; described the readout as a “worst-case outcome,” but argued it “should not completely rewrite the narrative.” [17]
- Leerink Partners: cut target to $195 from $227, maintained Outperform; pointed investors toward upcoming catalysts (including Arikayce ENCORE and other programs) despite the CRSsNP discontinuation. [18]
- Mizuho: reported target cut to $212 from $256 with an Outperform rating in coverage published today. [19]
- Wolfe Research: reduced price target sharply to $167 while maintaining Outperform, as referenced in multiple analyst-roundup notes. [20]
- Cantor Fitzgerald: maintained an Overweight stance with a $230 price target, per reporting that also cited prior expectations for CRSsNP peak sales. [21]
- BofA Securities: lowered target to $203 from $214 and kept a Buy rating, arguing the post-news selloff looked “overdone” in its commentary. [22]
- TD Cowen: published coverage indicating a $241 target after the miss (while maintaining a Buy/constructive stance, as reported in analyst-roundup notes). [23]
Zooming out from individual notes, MarketBeat’s compiled view (as displayed on Dec. 18) shows Insmed with a “Moderate Buy” consensus rating (based on 24 analyst ratings) and a consensus price target of $202.55, with targets ranging from $115 to $269. [24]
The key debate now: “one indication fail” vs. “signal about the drug”
The big intellectual fork in the road is whether the CRSsNP miss is best understood as:
A single-indication failure in a disease area that’s hard to model (Insmed itself highlighted the lack of animal models), or
a broader read-through on brensocatib’s ability to deliver symptom relief outside bronchiectasis.
Investors.com captured that tension in its Dec. 18 analysis, noting concerns about read-through to other indications like hidradenitis suppurativa (HS) (also described as lacking animal models), while emphasizing that analysts still pointed to other assets and launches as the core of the longer-term thesis. [25]
Mizuho’s coverage, cited by Fierce Pharma, took a harsher tone on the primary endpoint (“failed spectacularly,” in the analyst’s words) while still pointing to HS as a setting where the company remains optimistic, given the inflammatory biology involved (as described in that reporting). [26]
What’s next for Insmed: near-term catalysts after the Dec. 18 reset
Even after today’s drop, Insmed remains a story driven by commercial execution + clinical catalysts. Based on company updates earlier this year, the next major “watch items” include:
- BRINSUPRI (brensocatib) launch trajectory in NCFB: Insmed reported $28.1 million in BRINSUPRI revenue in Q3 2025, underscoring that the product is already commercial and no longer purely a “trial readout” story. [27]
- ARIKAYCE growth and label expansion efforts: Insmed reported $114.3 million in ARIKAYCE revenue in Q3 2025 and said it anticipated a Phase 3 ENCORE topline readout in the first half of 2026 in MAC lung disease patients who have not started antibiotics. [28]
- HS (hidradenitis suppurativa) data for brensocatib: In its October business update, Insmed said its Phase 2b CEDAR study was fully enrolled with topline data expected in the first half of 2026—a readout that could help answer whether today’s CRSsNP miss is a one-off or something more systematic. [29]
- International expansion for BRINSUPRI: Insmed previously said EU/UK/Japan regulatory submissions were progressing, with potential 2026 commercial launches pending approvals. [30]
- TPIP (treprostinil palmitil inhalation powder) Phase 3 plans: Insmed outlined Phase 3 plans across pulmonary hypertension and fibrotic lung diseases, which—if timelines hold—represent another major driver of future valuation beyond brensocatib’s label-expansion ambitions. [31]
One subtle “silver lining” some analysts raised: if CRSsNP had worked, Insmed might have needed a bigger commercial push (and potentially more discounting) to reach a broader population. With CRSsNP off the table, the company may be able to focus resources more tightly on bronchiectasis, ARIKAYCE, and pipeline assets—an argument cited in analyst commentary. [32]
Bottom line
Insmed stock’s December 18 drop is a classic biotech repricing: a clinical miss in a closely watched expansion indication triggered a rapid reset in forward revenue assumptions and sentiment. But the company is not a single-asset biotech—BRINSUPRI is already commercial in NCFB, ARIKAYCE is established, and INS1148 adds a fresh Phase 2–ready program aimed at ILD and asthma. [33]
For INSM investors, the market’s next questions are brutally simple (and therefore powerful): Can the company keep BRINSUPRI’s bronchiectasis launch momentum strong enough to offset the lost CRSsNP optionality—and can upcoming 2026 readouts reopen the growth narrative that today’s BiRCh miss cracked? [34]
References
1. www.sec.gov, 2. www.sec.gov, 3. www.fiercepharma.com, 4. www.sec.gov, 5. www.sec.gov, 6. m.investing.com, 7. investor.insmed.com, 8. www.sec.gov, 9. www.sec.gov, 10. www.barrons.com, 11. www.biopharmadive.com, 12. investor.insmed.com, 13. investor.insmed.com, 14. investor.insmed.com, 15. www.biopharmadive.com, 16. www.fiercepharma.com, 17. m.investing.com, 18. in.investing.com, 19. www.investing.com, 20. m.investing.com, 21. www.barrons.com, 22. www.streetinsider.com, 23. www.investing.com, 24. www.marketbeat.com, 25. www.investors.com, 26. www.fiercepharma.com, 27. investor.insmed.com, 28. investor.insmed.com, 29. investor.insmed.com, 30. investor.insmed.com, 31. investor.insmed.com, 32. www.investors.com, 33. www.sec.gov, 34. www.biopharmadive.com
