{"success":true,"data":{"pressRelease":{"id":"39355","rtpr_id":"nGNX3LKFQv","ticker":"GOSS","exchange":"NASDAQ","all_tickers":["GOSS"],"title":"Gossamer Bio, Inc. (GOSS) Faces Securities Class Action Amid 80% Drop On Phase 3 PROSERA Trial Failure – Hagens Berman","author":"Globe Newswire","published_at":"2026-05-19T13:00:16.104Z","article_body":"SAN FRANCISCO, May 19, 2026 (GLOBE NEWSWIRE) -- A securities class action\nlawsuit has been filed against Gossamer Bio, Inc. (NASDAQ: GOSS) and an\nexecutive, seeking to represent investors who purchased or otherwise acquired\nGossamer securities between June 16, 2025 and February 20, 2026.\n\nThe lawsuit follows Gossamer’s bombshell announcement on February 23, 2026\nthat top-line results for its Phase 3 PROSERA study did not meet the primary\nendpoint (the change from baseline in six-minute-walk distance at week 24).\nThe study evaluated seralutinib for the treatment of pulmonary arterial\nhypertension (“PAH”).\n\nThe developments, including the trial failure and 80% stock drop, prompted\nnational shareholder rights firm Hagens Berman to commence an investigation\ninto the alleged pending claims that Gossamer violated federal securities\nlaws. The firm encourages Gossamer investors who suffered substantial losses\non Class Period GOSS investments to submit your losses now\n(https://www.globenewswire.com/Tracker?data=gEFbORx7eLlIGO6MEhhOx16sLxWxQiQoZ8Q7wxVqZl4X4DaZsvYhvSNfggE-PDowDdfedicWv0DFkvqV_xvD22TqBekTGJk5-Ahh4Wenw90Yx5u5ZFpQtTlDo1VO0F3w).\n\nThe firm also encourages persons with knowledge who may be able to assist the\ninvestigation to contact its attorneys.\n\nView our latest video summary of the allegations: youtu.be/TOr_OsDdBXY\n(https://www.globenewswire.com/Tracker?data=r3l4vNaN4oySy5hB1jZm9a4roRIxMDKSxj6A3-6jrSDoYBD3VGZM7wd5z5uohaNBPpLkVuBEy0RbB-wkPVXmplDxCr-pXPD9o0NhTdXq6KQ=)\n\nClass Period: June 16, 2025 – Feb. 20, 2026\nLead Plaintiff Deadline: June 1, 2026\nVisit: www.hbsslaw.com/investor-fraud/goss \nContact the Firm Now: GOSS@hbsslaw.com \n844-916-0895\n\nGossamer Bio, Inc. (GOSS) Securities Class Action:\n\nThe litigation is focused on the propriety of Gossamer’s disclosures about\nthe Phase 3 PROSERA trial design, including its patient recruitment protocol\nand site-level monitoring.\n\nIn the past, Gossamer has emphasized that serlutinib is a “potential\nfirst-in-class therapeutic[,]” which “represents the possibility of a\nmulti-billion-dollar opportunity across multiple indications[.]”\n\nAs recently as mid-November 2025, the company’s management cited the highly\nsuccessful Merck Phase 3 STELLAR study of sotatercept for treating PAH.\nGossamer’s management said, “if you look at their data, the best\nperforming region was Latin America, and we have actually more patients coming\nfrom those same geographies and same sites.” Management also assured\ninvestors that “we have gone to the places where precedent studies have\nshown the greatest amount of efficacy, as well as having an entry criteria\nthat is ensuring that we have patients who, we believe, will really show an\nimprovement based upon, again background disease at week 24.”\n\nThe complaint alleges that, unknown to investors, Gossamer knew of or\nrecklessly disregarded the trial design issues with the Phase 3 PROSERA study\nand, instead, crafted a narrative assuring investors that it would meet its\nprimary endpoint. Also unknown to investors, patients at the study’s Latin\nAmerica sites were largely heavily-treated and performing particularly well on\nplacebo.\n\nInvestors’ expectations were dashed on February 23, 2026. That day, Gossamer\nannounced that PROSERA did not meet its primary endpoint and therefore\nefficacy was not statistically significant.\n\nManagement said during the conference call that day, “[t]he overall\ntreatment effect and statistical parameters were materially diluted by an\noutsize placebo response and meaningful regional heterogeneity, which\ncompressed the pool placebo-adjusted difference.” More specifically,\nmanagement revealed that in “Latin America, outsized placebo improvements\nmaterially compressed the pool treatment difference.”\n\nThe market swiftly reacted, sending the price of Gossamer shares down by 80%.\n\nAfter the Class Period, on April 9, 2026, the company revealed that since\nFebruary 24, 2026 it has not met the minimum share bid price ($1) required for\ncontinued listing on the Nasdaq Global Select Market.\n\n“We’re focused on whether Gossamer may have misled investors about the\nPROSERA trial design, including patient entry criteria, as alleged in the\npending lawsuit,” said Reed Kathrein\n(https://www.globenewswire.com/Tracker?data=16UqMPNqdFyHHMv3HEl4MZfmRfwxZUrE75hwOAoNQnEpOaHCwbNMtz_bgxsUGwUDF0WdPPrMRob3ddiWvTCRc7R1WtDTIejKiZLR1HIL3H-23qu1k34SYBsyYEmY2wUS),\nthe Hagens Berman partner leading the firm’s investigation.\n\nIf you invested in Gossamer Bio and have substantial losses, or have knowledge\nthat will assist the firm’s investigation, submit your losses now\n(https://www.globenewswire.com/Tracker?data=gEFbORx7eLlIGO6MEhhOx16sLxWxQiQoZ8Q7wxVqZl5uP7EplUYzmrn4JGQ44BTOBJqvHh5aZlL-FBBpkjlyToyiTWw5hHgUgZg_IP5DNNzb8DAGCRvlfl-2E3bVPPgE).\n\nIf you’d like more information and answers to additional frequently asked\nquestions about the Gossamer case and the firm’s investigation, read more\n(https://www.globenewswire.com/Tracker?data=gfkQHqPHZUJ2dKEW0EtpMJBDPes4VWmsCt5e4ZyA977jiIxqKMhT2Bw9I_9GgB5Jwk3P3POrMz99mtwEDehWXRo_8-rjYc75-lzI4i-ENnXcj6DiXH92gRmfY8S8P5mW7KOGrEcvCMv24Xx_D-xw5g==)\n»\n(https://www.globenewswire.com/Tracker?data=hq733_oeI-4X7DCnx0CedlxnhFk3Qn3VWpcXWKrhG9dnQmIdfHb6IhuvrPro8fsqYtECVDLyYDzQef-fDEYvWg7tZst-F7VcFwhVjkxW3ngd3C7REa-bpEMgFP9mslx0Ta_RDr4XxDvukKO86HNSjg==)\n\nWhistleblowers: Persons with non-public information regarding Gossamer Bio\nshould consider their options to help in the investigation or take advantage\nof the SEC Whistleblower program. Under the new program, whistleblowers who\nprovide original information may receive rewards totaling up to 30 percent of\nany successful recovery made by the SEC. For more information, call Reed\nKathrein at 844-916-0895 or email GOSS@hbsslaw.com.\n\nAbout Hagens Berman\n(https://www.globenewswire.com/Tracker?data=cVye9PaVZg9fpdTG3hQa9pwgdUbANKWNuppiZJjoCi7Jnn_9U_y0jTnHWaUoEjU9WY_DYhRfdEVDZOKB39cmIe7QHdPlgcbCD66ySGLr-HE=)\nHagens Berman is a global plaintiffs’ rights complex litigation firm\nfocusing on corporate accountability. The firm is home to a robust practice\nand represents investors as well as whistleblowers, workers, consumers and\nothers in cases achieving real results for those harmed by corporate\nnegligence and other wrongdoings. Hagens Berman’s team has secured more than\n$2.9 billion in this area of law. More about the firm and its successes can be\nfound at hbsslaw.com\n(https://www.globenewswire.com/Tracker?data=aVkEthUUkQwzroBGk5g2AlEXnM0UnlWibOtr8abMyEsJgtLOyBu3T7ADNrpR4Pxri_KgfCat_PMEefSDD8bKhQ==).\nFollow the firm for updates and news at @ClassActionLaw. \n\nContact: \nReed Kathrein, 844-916-0895\n\n(https://www.globenewswire.com/NewsRoom/AttachmentNg/2c81cd72-0ffb-43c9-9d0f-b622c3e44e43)\n\n\n\nGlobeNewswire, Inc. 2026","article_body_html":"","raw_payload":{"data":{"id":"nGNX3LKFQv","title":"Gossamer Bio, Inc. (GOSS) Faces Securities Class Action Amid 80% Drop On Phase 3 PROSERA Trial Failure – Hagens Berman","author":"Globe Newswire","ticker":"GOSS","created":"2026-05-19T13:00:16.104Z","tickers":["GOSS"],"exchange":"NASDAQ","article_body":"SAN FRANCISCO, May 19, 2026 (GLOBE NEWSWIRE) -- A securities class action\nlawsuit has been filed against Gossamer Bio, Inc. (NASDAQ: GOSS) and an\nexecutive, seeking to represent investors who purchased or otherwise acquired\nGossamer securities between June 16, 2025 and February 20, 2026.\n\nThe lawsuit follows Gossamer’s bombshell announcement on February 23, 2026\nthat top-line results for its Phase 3 PROSERA study did not meet the primary\nendpoint (the change from baseline in six-minute-walk distance at week 24).\nThe study evaluated seralutinib for the treatment of pulmonary arterial\nhypertension (“PAH”).\n\nThe developments, including the trial failure and 80% stock drop, prompted\nnational shareholder rights firm Hagens Berman to commence an investigation\ninto the alleged pending claims that Gossamer violated federal securities\nlaws. The firm encourages Gossamer investors who suffered substantial losses\non Class Period GOSS investments to submit your losses now\n(https://www.globenewswire.com/Tracker?data=gEFbORx7eLlIGO6MEhhOx16sLxWxQiQoZ8Q7wxVqZl4X4DaZsvYhvSNfggE-PDowDdfedicWv0DFkvqV_xvD22TqBekTGJk5-Ahh4Wenw90Yx5u5ZFpQtTlDo1VO0F3w).\n\nThe firm also encourages persons with knowledge who may be able to assist the\ninvestigation to contact its attorneys.\n\nView our latest video summary of the allegations: youtu.be/TOr_OsDdBXY\n(https://www.globenewswire.com/Tracker?data=r3l4vNaN4oySy5hB1jZm9a4roRIxMDKSxj6A3-6jrSDoYBD3VGZM7wd5z5uohaNBPpLkVuBEy0RbB-wkPVXmplDxCr-pXPD9o0NhTdXq6KQ=)\n\nClass Period: June 16, 2025 – Feb. 20, 2026\nLead Plaintiff Deadline: June 1, 2026\nVisit: www.hbsslaw.com/investor-fraud/goss \nContact the Firm Now: GOSS@hbsslaw.com \n844-916-0895\n\nGossamer Bio, Inc. (GOSS) Securities Class Action:\n\nThe litigation is focused on the propriety of Gossamer’s disclosures about\nthe Phase 3 PROSERA trial design, including its patient recruitment protocol\nand site-level monitoring.\n\nIn the past, Gossamer has emphasized that serlutinib is a “potential\nfirst-in-class therapeutic[,]” which “represents the possibility of a\nmulti-billion-dollar opportunity across multiple indications[.]”\n\nAs recently as mid-November 2025, the company’s management cited the highly\nsuccessful Merck Phase 3 STELLAR study of sotatercept for treating PAH.\nGossamer’s management said, “if you look at their data, the best\nperforming region was Latin America, and we have actually more patients coming\nfrom those same geographies and same sites.” Management also assured\ninvestors that “we have gone to the places where precedent studies have\nshown the greatest amount of efficacy, as well as having an entry criteria\nthat is ensuring that we have patients who, we believe, will really show an\nimprovement based upon, again background disease at week 24.”\n\nThe complaint alleges that, unknown to investors, Gossamer knew of or\nrecklessly disregarded the trial design issues with the Phase 3 PROSERA study\nand, instead, crafted a narrative assuring investors that it would meet its\nprimary endpoint. Also unknown to investors, patients at the study’s Latin\nAmerica sites were largely heavily-treated and performing particularly well on\nplacebo.\n\nInvestors’ expectations were dashed on February 23, 2026. That day, Gossamer\nannounced that PROSERA did not meet its primary endpoint and therefore\nefficacy was not statistically significant.\n\nManagement said during the conference call that day, “[t]he overall\ntreatment effect and statistical parameters were materially diluted by an\noutsize placebo response and meaningful regional heterogeneity, which\ncompressed the pool placebo-adjusted difference.” More specifically,\nmanagement revealed that in “Latin America, outsized placebo improvements\nmaterially compressed the pool treatment difference.”\n\nThe market swiftly reacted, sending the price of Gossamer shares down by 80%.\n\nAfter the Class Period, on April 9, 2026, the company revealed that since\nFebruary 24, 2026 it has not met the minimum share bid price ($1) required for\ncontinued listing on the Nasdaq Global Select Market.\n\n“We’re focused on whether Gossamer may have misled investors about the\nPROSERA trial design, including patient entry criteria, as alleged in the\npending lawsuit,” said Reed Kathrein\n(https://www.globenewswire.com/Tracker?data=16UqMPNqdFyHHMv3HEl4MZfmRfwxZUrE75hwOAoNQnEpOaHCwbNMtz_bgxsUGwUDF0WdPPrMRob3ddiWvTCRc7R1WtDTIejKiZLR1HIL3H-23qu1k34SYBsyYEmY2wUS),\nthe Hagens Berman partner leading the firm’s investigation.\n\nIf you invested in Gossamer Bio and have substantial losses, or have knowledge\nthat will assist the firm’s investigation, submit your losses now\n(https://www.globenewswire.com/Tracker?data=gEFbORx7eLlIGO6MEhhOx16sLxWxQiQoZ8Q7wxVqZl5uP7EplUYzmrn4JGQ44BTOBJqvHh5aZlL-FBBpkjlyToyiTWw5hHgUgZg_IP5DNNzb8DAGCRvlfl-2E3bVPPgE).\n\nIf you’d like more information and answers to additional frequently asked\nquestions about the Gossamer case and the firm’s investigation, read more\n(https://www.globenewswire.com/Tracker?data=gfkQHqPHZUJ2dKEW0EtpMJBDPes4VWmsCt5e4ZyA977jiIxqKMhT2Bw9I_9GgB5Jwk3P3POrMz99mtwEDehWXRo_8-rjYc75-lzI4i-ENnXcj6DiXH92gRmfY8S8P5mW7KOGrEcvCMv24Xx_D-xw5g==)\n»\n(https://www.globenewswire.com/Tracker?data=hq733_oeI-4X7DCnx0CedlxnhFk3Qn3VWpcXWKrhG9dnQmIdfHb6IhuvrPro8fsqYtECVDLyYDzQef-fDEYvWg7tZst-F7VcFwhVjkxW3ngd3C7REa-bpEMgFP9mslx0Ta_RDr4XxDvukKO86HNSjg==)\n\nWhistleblowers: Persons with non-public information regarding Gossamer Bio\nshould consider their options to help in the investigation or take advantage\nof the SEC Whistleblower program. Under the new program, whistleblowers who\nprovide original information may receive rewards totaling up to 30 percent of\nany successful recovery made by the SEC. For more information, call Reed\nKathrein at 844-916-0895 or email GOSS@hbsslaw.com.\n\nAbout Hagens Berman\n(https://www.globenewswire.com/Tracker?data=cVye9PaVZg9fpdTG3hQa9pwgdUbANKWNuppiZJjoCi7Jnn_9U_y0jTnHWaUoEjU9WY_DYhRfdEVDZOKB39cmIe7QHdPlgcbCD66ySGLr-HE=)\nHagens Berman is a global plaintiffs’ rights complex litigation firm\nfocusing on corporate accountability. The firm is home to a robust practice\nand represents investors as well as whistleblowers, workers, consumers and\nothers in cases achieving real results for those harmed by corporate\nnegligence and other wrongdoings. Hagens Berman’s team has secured more than\n$2.9 billion in this area of law. More about the firm and its successes can be\nfound at hbsslaw.com\n(https://www.globenewswire.com/Tracker?data=aVkEthUUkQwzroBGk5g2AlEXnM0UnlWibOtr8abMyEsJgtLOyBu3T7ADNrpR4Pxri_KgfCat_PMEefSDD8bKhQ==).\nFollow the firm for updates and news at @ClassActionLaw. \n\nContact: \nReed Kathrein, 844-916-0895\n\n(https://www.globenewswire.com/NewsRoom/AttachmentNg/2c81cd72-0ffb-43c9-9d0f-b622c3e44e43)\n\n\n\nGlobeNewswire, Inc. 2026"},"type":"article","timestamp":"2026-05-19T13:00:16.148949637Z","server_sent_at_ms":1779195616148},"received_at":"2026-05-19T13:00:16.205Z","source_url":null},"analysis":{"id":"28799","press_release_id":"39355","analysis_json":{"industry":{"label":"Biotechnology","sector":"Health Care"},"redFlags":["Stock dropped 80% following Phase 3 trial failure","Company failed to meet Nasdaq minimum bid price ($1) requirement for continued listing"],"eventType":"legal_litigation","narrative":"Hagens Berman issued a shareholder solicitation notice regarding the securities class action against Gossamer Bio following the failure of its Phase 3 PROSERA trial.\n\nThe firm encourages investors who purchased GOSS between June 16, 2025, and February 20, 2026, to submit their losses and contact the firm before the June 1, 2026, lead plaintiff deadline.\n\nThis release is marketing by the plaintiff's counsel, not a new disclosure from Gossamer Bio, and reflects the ongoing litigation stemming from the 80% stock drop after the trial missed its primary endpoint.","sentiment":"neutral","agentHooks":{"shouldPost":false,"suggestedAngle":"Plaintiff-firm solicitation -- suppress."},"keyFigures":{"customDimensions":{"stock_drop_pct":"80%","nasdaq_bid_price_threshold":"$1"}},"quotedText":"We’re focused on whether Gossamer may have misled investors about the PROSERA trial design, including patient entry criteria, as alleged in the pending lawsuit","namedEntities":{"people":[{"name":"Reed Kathrein","role":"Partner, Hagens Berman"}],"products":["seralutinib","sotatercept"],"companies":[{"name":"Gossamer Bio, Inc.","ticker":"GOSS","relationship":"defendant"},{"name":"Hagens Berman","relationship":"plaintiff law firm"},{"name":"Merck","relationship":"competitor"}],"dollarAmounts":[{"amount":"$1","context":"minimum share bid price for Nasdaq listing"},{"amount":"$2.9 billion","context":"total recovered by Hagens Berman in similar cases"}]},"materialImpact":{"score":1,"reasoning":"This is a plaintiff law-firm solicitation issued by Hagens Berman, not an issuer disclosure. It serves to recruit lead plaintiffs and investors for an existing class action following a known trial failure. Per guardrails, such solicitations are low-impact noise unless a class is certified or a major settlement is announced."},"tickerRelevance":{"others":[{"ticker":"MRK","relevance":"competitor"}],"primary":"GOSS"},"globalImportance":15,"audienceRelevance":10,"eventTypeSecondary":[],"importanceComponents":{"context":"Post-trial-failure litigation noise","tickerTier":"small-cap","eventGravity":"law-firm-solicitation","issuerAuthored":false}},"event_type":"legal_litigation","event_type_secondary":null,"sentiment":"neutral","material_impact_score":1,"narrative":"Hagens Berman issued a shareholder solicitation notice regarding the securities class action against Gossamer Bio following the failure of its Phase 3 PROSERA trial.\n\nThe firm encourages investors who purchased GOSS between June 16, 2025, and February 20, 2026, to submit their losses and contact the firm before the June 1, 2026, lead plaintiff deadline.\n\nThis release is marketing by the plaintiff's counsel, not a new disclosure from Gossamer Bio, and reflects the ongoing litigation stemming from the 80% stock drop after the trial missed its primary endpoint.","key_figures":{"customDimensions":{"stock_drop_pct":"80%","nasdaq_bid_price_threshold":"$1"}},"named_entities":{"people":[{"name":"Reed Kathrein","role":"Partner, Hagens Berman"}],"products":["seralutinib","sotatercept"],"companies":[{"name":"Gossamer Bio, Inc.","ticker":"GOSS","relationship":"defendant"},{"name":"Hagens Berman","relationship":"plaintiff law firm"},{"name":"Merck","relationship":"competitor"}],"dollarAmounts":[{"amount":"$1","context":"minimum share bid price for Nasdaq listing"},{"amount":"$2.9 billion","context":"total recovered by Hagens Berman in similar cases"}]},"model_name":"qwen3_6_27b_awq","prompt_hash":"sha256:727b4b9429a443af","schema_hash":"sha256:05005c02d9cffac9","created_at":"2026-05-19T13:06:45.643Z","global_importance":15,"audience_relevance":10,"importance_components":{"context":"Post-trial-failure litigation noise","tickerTier":"small-cap","eventGravity":"law-firm-solicitation","issuerAuthored":false}},"durationMs":24899,"modelName":"george-droid-qwen-72b"}}