Time-Sensitive: Allegations Focus on PROSERA Patient Selection Representations

NEW YORK , April 30, 2026 /PRNewswire/ -- SueWallSt alerts investors in Gossamer Bio, Inc. (NASDAQ: GOSS) that a pending securities class action seeks to recover damages for shareholders who purchased securities between June 16, 2025 and February 20, 2026.

Class Period: June 16, 2025 through February 20, 2026

Check if you can recover your investment losses  or contact Joseph E. Levi, Esq. at jlevi@SueWallSt.com | (888) SueWallSt.

Gossamer shares collapsed from $2.13 to $0.42, over an 80% single-day loss of $1.71 per share, after the Company revealed that its Phase 3 PROSERA trial failed to meet its primary endpoint. The Court has set June 1, 2026 as the deadline to apply for lead plaintiff appointment.

How the "Patient Selection Goal" Allegedly Misled the Market

The lawsuit asserts that management repeatedly told shareholders that PROSERA's enrollment strategy was "building on insights from the Phase 2 TORREY Study" and that the Company had "focused on selecting a patient population that aligns closely with the study's objectives." As alleged, these statements created the impression that enrolled patients matched the profile needed to demonstrate a clinically significant benefit at Week 24.

The action claims the reality was materially different. Latin American clinical sites enrolled a heavily-treated, lower-risk patient population whose baseline characteristics diverged from standard trial norms. According to the lawsuit, this divergence was not disclosed to investors despite being known or recklessly disregarded by the Company.

Enrollment Characteristics Versus TORREY Study Benchmarks

• 55% of PROSERA patients were on triple or quadruple background PAH therapy, creating a heavily-treated population profile
• 61% were on background prostacyclin therapy, further distinguishing this cohort from typical Phase III PAH baselines
• Latin American sites produced near-parity between placebo and treatment response rates, as alleged, compressing the measurable drug effect
• Management later acknowledged "a substantial number of super responders on placebo with over 100-meter walk improvements" at Latin American sites
• The Company itself admitted it was "still early in the investigation of what happened in Latin America"

"Investors deserve transparency about material risks that could affect their investments. When a company tells the market it has accomplished its patient selection goal, shareholders are entitled to rely on that representation when making investment decisions." -- Joseph E. Levi, Esq.

Speak with an attorney about recovering damages  or call (888) SueWallSt.

Why Enrollment Adequacy Allegedly Matters to Investors

In clinical-stage biopharmaceuticals, patient selection is among the most consequential design decisions for a pivotal trial. The lawsuit contends that by assuring investors the enrollment goal had been "accomplished" while the actual Latin American cohort characteristics created a high probability of outsized placebo response, management provided the market with a materially incomplete picture of PROSERA's risk profile. The resulting +13.3 meter placebo-adjusted gain fell short of the pre-specified 0.025 alpha threshold, producing a p-value of 0.0320 that narrowly missed statistical significance.

WHY SUEWALLST -- Ranked in ISS Securities Class Action Services' Top 50 Report for seven consecutive years, SueWallSt is a nationally recognized leader in shareholder rights litigation. With a team of over 70 professionals, the firm has recovered hundreds of millions of dollars for investors.

Frequently Asked Questions About the GOSS Lawsuit

Q: Who is eligible to join the GOSS investor lawsuit? A: Investors who purchased GOSS stock or securities between June 16, 2025 and February 20, 2026 and suffered financial losses may be eligible. Eligibility is based on purchase date and documented losses, not on whether you still hold the shares.

Q: How much did GOSS stock drop? A: Shares fell approximately 80%, a decline of $1.71 per share, after the Company disclosed that its Phase 3 PROSERA study failed to meet the primary endpoint. Investors who purchased shares during the class period at artificially inflated prices may be entitled to compensation.

Q: What specific misstatements does the GOSS lawsuit allege? A: The complaint allegesGossamer Bio made materially false or misleading statements regarding the quality of patient enrollment in the PROSERA trial and the alignment of that enrollment with Phase 2 TORREY Study insights. When the true state was revealed, the stock price declined sharply.

Q: What do GOSS investors need to do right now? A: Gather brokerage records including purchase dates, share quantities, and prices paid. Contact SueWallSt for a free, no-obligation evaluation at jlevi@SueWallSt.com or (888) SueWallSt. 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 them. 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:
SueWallSt
Joseph E. Levi, Esq.
Ed Korsinsky, Esq.
33 Whitehall Street, 27th Floor
New York, NY 10004
jlevi@SueWallSt.com
Tel: (888) SueWallSt
Fax: (212) 363-7171

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SOURCE SueWallSt.com