Gossamer Bio, Inc. Securities Class Action Lawsuit: Investors With Losses May Seek Lead Plaintiff Status

The Gross Law Firm has issued a notice to shareholders of Gossamer Bio, Inc. (NASDAQ: GOSS) regarding a potential securities class action and the process for seeking appointment as lead plaintiff.

Class period and who may be eligible

The class period is June 16, 2025 to February 20, 2026. Shareholders who purchased shares of GOSS during this period are encouraged to contact the firm regarding possible lead plaintiff appointment. Appointment as lead plaintiff is not required to participate in any recovery.

Allegations in the complaint

According to the complaint, the defendants allegedly provided “overwhelmingly positive” statements to investors while, at the same time, disseminating false and misleading statements and/or concealing material adverse facts. The allegations focus on the study design for the Company’s Phase 3 PROSERA study, particularly controlling for the placebo response at Latin American testing sites.

Key event and market reaction

On February 23, 2026, Gossamer published a press release and hosted a Special Call announcing topline results for its Phase 3 PROSERA study. The study allegedly failed to meet the primary endpoint of improved six-minute walk distance (6MWD) at Week 24, with a +13.3 meter placebo-adjusted gain (p-0.0320) that did not meet the required 0.025 alpha threshold.

The notice states that Gossamer attributed the miss to patients at Latin American sites performing particularly well on placebo, due to enrollment of a heavily treated lower-risk population.

Following this news, the price of Gossamer’s common stock declined from a closing market price of $2.13 per share on February 20, 2026 to $0.42 per share on February 23, 2025, a decline of over 80% in a single day.

Deadline and next steps

The deadline to seek to be a lead plaintiff is June 1, 2026. Shareholders are encouraged not to delay in registering for the class action.

After registering as a shareholder who purchased shares of GOSS during the class period, the notice says shareholders will be enrolled in a portfolio monitoring software system to receive status updates throughout the lifecycle of the case. The notice states there is no cost or obligation to participate.

Contact information

The Gross Law Firm
15 West 38th Street, 12th floor
New York, NY, 10018

Email: dg@securitiesclasslaw.com
Phone: (646) 453-8903

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