GOSS Investor Alert: Gossamer Bio Securities Fraud Lawsuit - Investors With Losses May Seek to Lead the Class Action After Allegedly Concealing PROSERA Trial Risks: Levi & Korsinsky

Key Dates and Disclosure Events Shareholders Need to Know

NEW YORK , May 6, 2026 /PRNewswire/ -- Levi & Korsinsky, LLP encourages investors who suffered losses in Gossamer Bio, Inc. (NASDAQ: GOSS) to contact the firm. WHO IS AFFECTED: Those who purchased GOSS securities between June 16, 2025, and February 20, 2026, may be entitled to recover damages. Find out if you are eligible to recover losses  or contact Joseph E. Levi, Esq. at jlevi@levikorsinsky.com  or (212) 363-7500.

Gossamer shares collapsed over 80%, falling $1.71 per share from $2.13 to $0.42 in a single trading session after the Company revealed its Phase 3 PROSERA study failed to meet its primary endpoint. The window to apply for lead plaintiff closes on June 1, 2026.

June 16, 2025: Enrollment Completed, Confidence Projected

Gossamer announced the completion of enrollment in its registrational Phase 3 PROSERA study evaluating seralutinib for pulmonary arterial hypertension. Management stated it had accomplished its "patient selection goal" and that the enrolled population "aligns closely with the study's objectives." No mention was made of risks arising from the composition of patients enrolled at Latin American clinical sites, the lawsuit contends.

August 5, 2025: Operational Excellence Narrative Reinforced

In its second quarter earnings release, the Company described its approach to the PROSERA study as driven by "discipline and operational excellence" and expressed "conviction around the strength of the science." The securities action alleges that this characterization concealed growing execution risks at international trial sites.

November 5, 2025: Final Quarter Update Before Readout

Gossamer issued a third quarter update describing the study as progressing through its "final stages" and expressing pride in its team's "focus, diligence, and professionalism." The complaint asserts that by this point, the Company had access to enrollment and baseline data that should have revealed the risk profile of its Latin American patient cohort.

February 23, 2026: The Over 80% Single-Day Collapse

Gossamer disclosed topline Phase 3 results showing a +13.3 meter placebo-adjusted 6MWD gain with a p-value of 0.0320, failing to clear the pre-specified 0.025 alpha threshold. On an associated Special Call, management attributed the miss to "outsized" placebo improvements at Latin American sites, where heavily-treated, lower-risk patients performed unexpectedly well on placebo. One analyst noted the data irregularity pointed to potential "human measurement error during 6MWD lap counting."

Chronology of Alleged Disclosure Failures

• June 16, 2025: Enrollment completion announced with no disclosure of Latin American patient composition risks
• August 5, 2025: "Operational excellence" characterization  allegedly masked site monitoring concerns
• November 5, 2025: "Final stages" update omitted known baseline data showing atypical enrollment characteristics
• February 23, 2026: Topline results revealed primary endpoint failure and outsized placebo response
• February 24, 2026: Wedbush downgraded GOSS to Neutral and slashed its price target from $6 to $1
• March 5, 2026: Oppenheimer reduced its price target from $12 to $3, citing "trial execution issue"

"Timely disclosure of material developments is fundamental to fair and efficient markets. The chronology in this case raises questions about whether shareholders received accurate information at critical junctures during the PROSERA study."  -- Joseph E. Levi, Esq.

Submit your claim before the deadline  or call Joseph E. Levi, Esq. at (212) 363-7500.

ABOUT THE FIRM  -- For over two decades, Levi & Korsinsky has represented shareholders in securities class actions. Ranked in ISS Top 50 for seven consecutive years. Those wishing to serve as lead plaintiff must act by June 1, 2026.

Frequently Asked Questions About the GOSS Lawsuit

Q: When did Gossamer Bio allegedly mislead investors?  A: The class period runs from June 16, 2025, through February 20, 2026. The alleged fraud was revealed through corrective disclosures on February 23, 2026, causing a single-day stock decline of over 80%.

Q: What specific misstatements does the GOSS lawsuit allege ?  A: The complaint alleges Gossamer made materially false or misleading statements regarding the Phase 3 PROSERA trial design, particularly by failing to disclose that heavily-treated, lower-risk patients at Latin American sites created a high risk of an outsized placebo response that would jeopardize the primary endpoint.

Q: What do GOSS investors need to do right now?  A: Gather brokerage records including purchase dates, share quantities, and prices paid. Contact Levi & Korsinsky for a free, no-obligation evaluation at jlevi@levikorsinsky.com  or (212) 363-7500. No immediate action is required to remain eligible as a class member.

Q: What if I already sold my GOSS shares -- can I still recover losses?  A: Yes. Eligibility is based on when you purchased, not whether you still hold shares. Investors who bought during the class period and sold at a loss may still participate.

Q: What does it cost me to participate?  A: Nothing. Securities class actions are handled on a pure contingency basis. No upfront fees, no retainer, no out-of-pocket costs.

Q: What if I missed the lead plaintiff deadline?  A: The deadline applies only to investors seeking lead plaintiff appointment. Class members who miss it can still participate in any settlement or recovery.

CONTACT:

Levi & Korsinsky, LLP

Joseph E. Levi, Esq.

Ed Korsinsky, Esq.

33 Whitehall Street, 27th Floor

New York, NY 10004

jlevi@levikorsinsky.com

Tel: (212) 363-7500

Fax: (212) 363-7171

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SOURCE Levi & Korsinsky, LLP