Gossamer Bio, Inc.

Gossamer Bio, Inc. is a clinical-stage biopharmaceutical company focused on the development and commercialization of seralutinib for the treatment of pulmonary hypertension (PH), specifically pulmonary arterial hypertension (PAH) and PH associated with interstitial lung disease (PH-ILD) [Item 1, Business — Overview]. The company's goal is to be an industry leader in PH and enhance patients' lives, achieved by assembling an experienced team of industry veterans, scientists, clinicians, and key opinion leaders [Item 1, Business — Overview].

The core business model revolves around the development and potential commercialization of seralutinib, an investigational inhaled small molecule inhibitor, and RT234, an investigational inhaled, on-demand PDE5 inhibitor [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor); Item 1, Business — RT234 (Inhaled, On-Demand PDE5 Inhibitor)]. Revenue is currently generated from a collaboration agreement with Chiesi, which includes a one-time development cost reimbursement payment for licenses and ongoing cost-sharing payments for research and development services [Item 7, MD&A — Revenue]. The company aims to generate future revenue from license fees, upfront payments, milestone payments, product sales, and royalties [Item 7, MD&A — Revenue].

Seralutinib (GB002) is an investigational inhaled, small molecule, platelet-derived growth factor receptor (PDGFR), colony-stimulating factor 1 receptor (CSF1R), and c-KIT inhibitor [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)]. It is currently being evaluated in a Phase 3 clinical trial for PAH, with the belief that it can reverse pathological remodeling by addressing underlying mechanisms [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)]. In February 2026, topline results from the 48-week Phase 3 PROSERA Trial in 390 PAH patients showed a placebo-adjusted improvement in the primary endpoint, six-minute walk distance (6MWD) at Week 24, of 13.3 meters (p = 0.0320), which missed the prespecified alpha threshold of 0.025 [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)]. However, in the prespecified intermediate- and high-risk subgroup (n = 234), a 20.0m placebo-adjusted improvement in 6MWD (nominal p = 0.0207) was observed [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)]. Additionally, in patients with connective tissue disease-associated PAH (CTD-APAH) (n = 87), seralutinib demonstrated a placebo-adjusted improvement in 6MWD at Week 24 of 37.0 meters (nominal p = 0.0104) [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)]. Seralutinib has received orphan drug designation for PAH from the FDA, EC, and PMDA of Japan [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)].

RT234 is an investigational inhaled, as-needed (PRN), dry-powder formulation of vardenafil, a PDE5 inhibitor, being developed for PAH and PH-ILD [Item 1, Business — RT234 (Inhaled, On-Demand PDE5 Inhibitor)]. It has completed open-label Phase 2 clinical trials and aims to address an unmet need for on-demand symptom management, complementing existing chronic PH therapies [Item 1, Business — RT234 (Inhaled, On-Demand PDE5 Inhibitor)]. The company entered into an option agreement with Respira Therapeutics in September 2025 to acquire RT234 [Item 1, Business — RT234 (Inhaled, On-Demand PDE5 Inhibitor)].

For the fiscal year ended December 31, 2025, total revenue was $48.471 million [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. Research and development expenses were $174.093 million [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. In process research and development expenses were $7.475 million [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. General and administrative expenses totaled $37.631 million [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. The company reported a net loss of $170.370 million [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. As of December 31, 2025, cash, cash equivalents, and marketable securities were $136.9 million [Item 7, MD&A — Liquidity and Capital Resources], and the accumulated deficit was $1,438.9 million [Item 7, MD&A — Overview]. The company has $200.0 million in aggregate principal amount of 5.00% convertible senior notes due 2027 [Item 1A, Risk Factors — Risks Related to Our Limited Operating History, Financial Position and Capital Requirements].

Comparing 2025 to 2024, total revenue decreased by $66.230 million, primarily due to a $90.682 million decrease from the sale of licenses, partially offset by a $24.452 million increase in revenue from contracts with collaborators [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. Research and development expenses increased by $35.606 million, mainly driven by a $44.4 million increase in clinical trial costs for seralutinib, offset by a $9.2 million decrease in costs for terminated programs [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. General and administrative expenses increased by $1.498 million, primarily due to a $6.3 million increase in commercial planning expense and a $1.2 million increase in personnel expense, offset by a $5.1 million decrease in stock-based compensation and a $1.1 million decrease in facilities expense [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024]. Other income, net, decreased by $4.0 million, mainly due to a $6.4 million decrease in investment accretion, partially offset by a $0.5 million decrease in interest expense and a $1.1 million increase in other income [Item 7, MD&A — Results of Operations for the Years Ended December 31, 2025 and 2024].

In May 2024, Gossamer Bio entered into a collaboration agreement with Chiesi for the development and commercialization of seralutinib [Item 1, Business — License and Collaboration Agreements]. Under this agreement, Gossamer Bio leads global development of seralutinib in PAH and PH-ILD and will lead potential commercialization in the United States, with both parties contributing 50% of commercial efforts [Item 1, Business — License and Collaboration Agreements]. Chiesi will lead global development in additional indications and commercialization in the United States for those indications, and has exclusive commercialization rights outside the United States [Item 1, Business — License and Collaboration Agreements]. In September 2025, the company entered into an option agreement with Respira Therapeutics to acquire RT234 [Item 1, Business — RT234 (Inhaled, On-Demand PDE5 Inhibitor)]. Following the February 2026 announcement of PROSERA topline results, the company paused enrollment in the SERANATA Phase 3 study in PH-ILD to evaluate the PROSERA dataset and support disciplined resource allocation [Item 1, Business — Summary of Paused SERANATA Phase 3 Clinical Trial in PH-ILD]. In March 2026, the company announced a workforce reduction of approximately 77 individuals, representing approximately 48% of its total workforce, to preserve cash [Item 1A, Risk Factors — We may not realize the expected benefits from our recent workforce reduction].

Gossamer Bio's near-term strategy is to focus resources on advancing seralutinib for PAH and pursue regulatory alignment and potential approval as efficiently as possible [Item 1, Business — Our Strategy]. Following the February 2026 announcement of PROSERA topline results, the company is prioritizing (i) completing in-depth analyses of the PROSERA dataset, (ii) engaging with the U.S. Food and Drug Administration (FDA) to obtain feedback regarding potential regulatory paths forward, and (iii) evaluating strategic options and resource allocation, in addition to strengthening its capital structure [Item 1, Business — Our Strategy]. The company plans to engage with the FDA, including through requesting a Type C meeting, to understand their perspective on the totality of the PROSERA and TORREY datasets and potential regulatory paths forward [Item 1, Business — Our Strategy]. The decision to submit a New Drug Application (NDA) and its timing will be informed by ongoing analyses of the PROSERA dataset, the totality of clinical data, and FDA feedback [Item 1, Business — Our Strategy]. While timing is subject to FDA feedback and other variables, the company currently anticipates a potential approval action date by year-end 2027 [Item 1, Business — Our Strategy].

The company continues to believe seralutinib may have meaningful potential in fibrotic lung disease, including PH-ILD, informed by the connective tissue disease-associated PAH (CTD-APAH) findings in PROSERA [Item 1, Business — Our Strategy]. The subgroup of patients with CTD-APAH (n = 87) in PROSERA demonstrated a placebo-adjusted improvement in 6MWD at Week 24 of 37.0 meters (nominal p = 0.0104) [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)]. The company believes the biology of CTD-APAH may be relevant to broader fibrotic lung disease populations, including PH-ILD [Item 1, Business — Seralutinib (Inhaled PDGFR, CSF1R and c-KIT Inhibitor)]. However, enrollment in the SERANATA Phase 3 study in PH-ILD has been paused to support disciplined resource allocation and to evaluate the implications of PROSERA as the company engages with regulators [Item 1, Business — Our Strategy].

Regarding operational outlook, the company intends to maintain disciplined resource allocation while advancing toward potential approval [Item 1, Business — Our Strategy]. The ongoing open-label extension studies for seralutinib remain active, with continued follow-up intended to further characterize longer-term exposure and potential durability of effect [Item 1, Business — Our Strategy]. The company also plans to advance RT234 under its option agreement with Respira Therapeutics in a capital-efficient manner, structured to support limited foundational manufacturing and device readiness activities [Item 1, Business — Our Strategy]. RT234 could be ready to re-enter clinical development as early as 2027 [Item 1, Business — Our Strategy].

Planned capital allocation includes evaluating a range of potential alternatives related to the outstanding convertible notes to support strategic priorities [Item 1, Business — Our Strategy]. The company may also seek to raise additional capital through equity offerings, debt financings, or other capital sources [Item 1, Business — Our Strategy]. As of December 31, 2025, the company had $136.9 million in cash, cash equivalents, and marketable securities [Item 7, MD&A — Liquidity and Capital Resources]. The company believes these existing funds will be sufficient to fund operations into the first quarter of 2027 [Item 1A, Risk Factors — Risks Related to Our Limited Operating History, Financial Position and Capital Requirements]. However, additional capital will be required to support any additional development mandated by the FDA prior to any NDA submission [Item 1A, Risk Factors — Risks Related to Our Limited Operating History, Financial Position and Capital Requirements].

Management has explicitly flagged several structural headwinds and execution risks. The results from the PROSERA Phase 3 clinical trial may not be sufficient to support FDA approval or continued development of seralutinib, which would materially and adversely harm the business [Item 1A, Risk Factors — The results from the PROSERA Phase 3 clinical trial may not be sufficient to support FDA approval or continued development of seralutinib, which would materially and adversely harm our business]. The FDA has substantial discretion and may require additional preclinical, clinical, or other trials, resulting in additional development costs and significant delays [Item 1A, Risk Factors — The results from the PROSERA Phase 3 clinical trial may not be sufficient to support FDA approval or continued development of seralutinib, which would materially and adversely harm our business]. There is no assurance that any future trials will be successful [Item 1A, Risk Factors — The results from the PROSERA Phase 3 clinical trial may not be sufficient to support FDA approval or continued development of seralutinib, which would materially and adversely harm our business]. The recent workforce reduction of approximately 77 individuals, or 48% of the total workforce, may not yield expected benefits, including cash conservation, and could make it difficult to retain key personnel, leading to loss of institutional knowledge and decreased morale [Item 1A, Risk Factors — We may not realize the expected benefits from our recent workforce reduction]. The company is entirely dependent on the success of seralutinib, and if it is unable to advance it through clinical development, obtain regulatory approval, or commercialize it, the business will be materially harmed [Item 1A, Risk Factors — We depend entirely on the success of seralutinib, which is currently in Phase 3 clinical development].

Gossamer Bio faces material risks across several categories. Macroeconomic risks include the need for substantial additional financing to achieve its goals, with existing cash, cash equivalents, and marketable securities only expected to fund operations into the first quarter of 2027 [Item 1A, Risk Factors — We will require substantial additional financing to achieve our goals]. Failure to obtain necessary capital on acceptable terms could force delays or termination of development programs [Item 1A, Risk Factors — We will require substantial additional financing to achieve our goals]. The company's $200.0 million in 5.00% convertible senior notes due 2027 pose a refinancing risk, and inability to repay or refinance could lead to restructuring, additional dilutive equity, asset sales, or bankruptcy [Item 1A, Risk Factors — Our indebtedness and liabilities could limit the cash flow available for our operations, expose us to risks that could adversely affect our business, financial condition and results of operations and impair our ability to satisfy our obligations under the notes]. Geopolitical events, such as military conflicts, and their associated sanctions and economic countermeasures, could disrupt supply chains or clinical trial activities [Item 1A, Risk Factors — We are subject to U.S. and certain foreign export and import controls, sanctions, embargoes, anti-corruption laws and anti-money laundering laws and regulations]. Regulatory risks are significant, as the Phase 3 PROSERA clinical trial for seralutinib did not meet its primary endpoint, and the FDA may require additional trials or deem the data insufficient for approval, leading to delays or inability to commercialize [Item 1A, Risk Factors — The results from the PROSERA Phase 3 clinical trial may not be sufficient to support FDA approval or continued development of seralutinib, which would materially and adversely harm our business]. Seralutinib is a combination product (drug and device), requiring coordinated review by different FDA centers, which may delay approval [Item 1A, Risk Factors — We depend entirely on the success of seralutinib, which is currently in Phase 3 clinical development]. Post-approval, the company would be subject to ongoing regulatory obligations, including potential restrictions on marketing or withdrawal from the market, and penalties for non-compliance [Item 1A, Risk Factors — Even if we receive regulatory approval for seralutinib, we will be subject to ongoing regulatory obligations and continued regulatory review, which may result in significant additional expense]. Operational risks include the reliance on third parties for clinical trials and manufacturing, where any failure to comply with Good Clinical Practice (GCP) or current Good Manufacturing Practice (cGMP) could delay or prevent regulatory approval [Item 1A, Risk Factors — We rely on third parties to conduct many of our clinical trials and preclinical studies]. The recent workforce reduction of approximately 48% of the total workforce, or 77 individuals, could lead to loss of institutional knowledge and decreased morale [Item 1A, Risk Factors — We may not realize the expected benefits from our recent workforce reduction]. Product liability lawsuits, with current insurance coverage of approximately $10 million, represent a risk that could result in substantial liabilities exceeding coverage [Item 1A, Risk Factors — If product liability lawsuits are brought against us, we may incur substantial liabilities and may be required to limit commercialization of seralutinib].

Management's message to shareholders emphasizes a strategic pivot following the topline results of the Phase 3 PROSERA study, which did not meet its primary endpoint [Item 1, Business — Our Strategy]. Despite this, management believes seralutinib demonstrates a risk-benefit profile that supports continued regulatory dialogue [Item 1, Business — Our Strategy]. The company's strategic priorities for the period ahead include completing in-depth analyses of the PROSERA dataset, engaging with the FDA to define potential regulatory paths forward, and evaluating strategic options and resource allocation, alongside strengthening the capital structure [Item 1, Business — Our Strategy]. Management anticipates a potential approval action date by year-end 2027, subject to FDA feedback and other variables [Item 1, Business — Our Strategy]. To support these priorities and conserve cash, the company has implemented a workforce reduction of approximately 77 individuals, or 48% of its total workforce, which is expected to be substantially completed by the end of May 2026 [Item 9B, Other Information]. Management also highlights the continued belief in seralutinib's potential in fibrotic lung disease, including PH-ILD, informed by the CTD-APAH findings in PROSERA, despite pausing enrollment in the SERANATA Phase 3 study [Item 1, Business — Our Strategy].