Gossamer Bio (4GB0) Risk Analysis

We are currently conducting, and may in the future conduct, one or more of our clinical trials for seralutinib outside the United States. The acceptance of study data from clinical trials conducted outside the U.S. or another jurisdiction by the FDA or comparable foreign regulatory authority may be subject to certain conditions or may not be accepted at all. In cases where data from foreign clinical trials are intended to serve as the sole basis for marketing approval in the U.S., the FDA will generally not approve the application on the basis of foreign data alone unless (i) the data are applicable to the U.S. population and U.S. medical practice; (ii) the trials were performed by clinical investigators of recognized competence and pursuant to GCP regulations; and (iii) the data may be considered valid without the need for an on-site inspection by the FDA, or if the FDA considers such inspection to be necessary, the FDA is able to validate the data through an on-site inspection or other appropriate means. In addition, for such clinical trials not subject to an IND, the FDA will not accept the data as support for an application for marketing approval unless the study was conducted in accordance with GCP requirements, and the FDA is able to validate the data from the study through an onsite inspection if deemed necessary. Many foreign regulatory authorities have similar approval requirements. In addition, such foreign trials would be subject to the applicable local laws of the foreign jurisdictions where the trials are conducted. There can be no assurance that the FDA or any comparable foreign regulatory authority will accept data from trials conducted outside of the U.S. or the applicable jurisdiction. If the FDA or any comparable foreign regulatory authority does not accept such data, it would result in the need for additional trials, which could be costly and time-consuming, and which may result in seralutinib not receiving approval for commercialization in the applicable jurisdiction. Conducting clinical trials outside the United States also exposes us to additional risks, including risks associated with: - additional foreign regulatory requirements;- foreign exchange fluctuations;- compliance with foreign manufacturing, customs, shipment and storage requirements;- cultural differences in medical practice and clinical research;- diminished protection of intellectual property in some countries; and - interruptions or delays in our trials resulting from geopolitical events, such as war or terrorism.

Regulatory authorities in some jurisdictions, including the United States and the EU, may designate drugs for relatively small patient populations as orphan drugs. Under the Orphan Drug Act of 1983, the FDA may designate a product as an orphan product if it is intended to treat a rare disease or condition, which is generally defined as a patient population of fewer than 200,000 individuals in the United States, or a patient population of greater than 200,000 individuals in the United States, but for which there is no reasonable expectation that the cost of developing the drug will be recovered from sales in the United States. In the EU, the EC grants orphan designation based on the EMA's Committee for Orphan Medicinal Products' opinion to promote the development of products (1) that are intended for the diagnosis, prevention or treatment that is life-threatening or chronically debilitating, and (2) either (a) such condition affects no more than five in 10,000 persons in the EU when the application is made, or (b) the product, without the benefits derived from orphan status, would be unlikely to generate sufficient returns in the EU to justify the necessary investment, and (3) there exists no satisfactory method of diagnosis, prevention or treatment of such condition authorized for marketing in the EU, or, if such a method exists, the medicine must be of significant benefit to those affected by the condition. We have received orphan drug designation in the United States, the EU and Japan for seralutinib for treatment of PAH and may seek additional orphan designations for seralutinib in the future. There can be no assurance that we will be able to maintain or obtain such designations. In the United States, orphan designation entitles a party to financial incentives such as opportunities for grant funding toward clinical trial costs, tax advantages and user-fee waivers. In addition, if a product candidate that has orphan designation subsequently receives the first FDA approval for the disease or condition for which it has such designation, the product is entitled to orphan drug exclusivity, which means that the FDA may not approve any other applications, including an NDA, to market the same drug for the same indication or use within the relevant disease or condition for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan drug exclusivity within the relevant indication or use or where the manufacturer is unable to assure sufficient product quantity to meet the needs relating to the indication or use protected by orphan exclusivity. Upon grant of a marketing authorization in the EU, orphan medicinal products are entitled to ten years of market exclusivity, during which time no similar medicinal product for the same indication may be placed on the market. This period may be reduced to six years if, at the end of the fifth year, it is established that the product no longer meets the orphan designation criteria, including where it is shown that the product is sufficiently profitable not to justify maintenance of market exclusivity or where the prevalence of the condition has increased above the threshold. Even if we obtain orphan drug exclusivity for a product, that exclusivity may not effectively protect the product from competition because different drugs can be approved for the same indications or uses. Even after an orphan drug is approved, the FDA or comparable foreign regulatory authority can subsequently approve the same drug for the same indication or use if such regulatory authority concludes that the later drug is clinically superior if it is shown to be safer, more effective or makes a major contribution to patient care with respect to the indication or use covered by orphan exclusivity. Orphan drug designation neither shortens the development time or regulatory review time of a drug nor gives the drug any advantage in the regulatory review or approval process.

In February 2026, we announced topline results from the Phase 3 PROSERA clinical trial of seralutinib in PAH, including that the study did not meet its primary endpoint. Following a Pre-NDA Type B meeting with the FDA held in mid-June 2026 and receipt of the official meeting minutes, we plan to proceed with an NDA submission for seralutinib for the treatment of PAH in September 2026. Based on the meeting minutes, the FDA characterized the degree of statistical significance and the magnitude of the treatment effect observed in PROSERA as review issues rather than filing issues. The Company's planned NDA submission is based in part on its views following its meeting with the FDA and the official minutes therefrom, and later feedback from, or developments with, the FDA may be inconsistent with such meeting or the Company's views from such meeting. The FDA's ultimate determination on approvability will be made upon review of the complete NDA, and there can be no assurance that the FDA will accept the NDA for filing or ultimately approve seralutinib. In general, the FDA has substantial discretion in the approval process and may decide that the totality of our datasets, including the Phase 3 PROSERA and Phase 2 TORREY studies, have not demonstrated a favorable overall benefit-risk assessment or may otherwise determine are insufficient for approval and require additional clinical trials or other studies, especially given that the PROSERA study did not meet its primary endpoint. Any such decision or feedback from the FDA would result in additional development costs and could significantly delay the potential for regulatory approval, or even if we are approved, a more narrow or limited labeled indication. We also may be unable to identify a viable development path towards approval for seralutinib, based on FDA feedback, our internal analysis of the data and market opportunity, or other factors. Even if we do identify a path to approval for seralutinib, we may require substantial additional capital and other resources to pursue such a path, and may be unable to raise such capital in the amounts needed or on attractive terms. There is also no assurance that any future trials or studies we may need to conduct will be successful. We may also pursue business development arrangements or other strategic collaborations; however, we may be unable to secure such arrangements on a timely basis or at all. If we are unable to develop or seek marketing approval for seralutinib or secure other strategic arrangements with third parties, or if we experience delays as a result of any of the above factors or otherwise, our business would be significantly harmed.

We have limited experience as a company in preparing, submitting marketing applications and have not previously submitted an NDA or other comparable foreign application for any product candidate. While our primary focus is on seeking approval from the FDA for seralutinib in PAH, we may also conduct a number of clinical trials for seralutinib in parallel over the next several years, which may be a difficult process to manage with our limited resources and which may divert the attention of management. In addition, we have had limited interactions with the FDA and cannot be certain our data from our Phase 2 and Phase 3 clinical trials of seralutinib will be sufficient to support an NDA submission in PAH, even if we believe the results are sufficiently positive to support a regulatory approval. Consequently, we may be unable to successfully and efficiently execute and complete necessary clinical trials in a way that leads to regulatory submission and approval of seralutinib. We may require more time and incur greater costs than our competitors and may not succeed in obtaining regulatory approvals of seralutinib.

As is the case with pharmaceuticals generally, it is likely that there may be side effects and adverse events associated with seralutinib's use. Results of our clinical trials could reveal a high and unacceptable severity and prevalence of side effects or unexpected characteristics. Undesirable side effects caused by seralutinib could cause us or regulatory authorities to interrupt, delay or halt clinical trials and could result in a more restrictive label or the delay or denial of regulatory approval by the FDA or comparable foreign regulatory authorities. For example, transaminase elevations of three times or greater of the upper limit of normal were observed in 13% of patients receiving seralutinib, as compared to 1% of patients receiving placebo in our PROSERA Phase 3 clinical trial, and although we believe PAH clinicians are well-accustomed to administering and monitoring therapies with potential hepatic effects, such adverse events could adversely affect the development of seralutinib or otherwise impair any commercialization efforts for seralutinib, if approved. Drug-related side effects could affect patient recruitment or the ability of enrolled patients to complete the trial or result in potential product liability claims. Any of these occurrences may harm our business, financial condition and prospects significantly. Moreover, if seralutinib is associated with undesirable side effects in clinical trials or have characteristics that are unexpected, we may elect to abandon its development or limit its development to more narrow uses or subpopulations in which the undesirable side effects or other characteristics are less prevalent, less severe or more acceptable from a risk-benefit perspective, which may limit the commercial expectations for seralutinib if approved. We may also be required to modify our study plans based on findings in our ongoing clinical trials. For example, although we believe seralutinib has been generally well tolerated in completed clinical trials, with cough, headache and transaminase elevations being the most common treatment emergent adverse effects in our PROSERA Phase 3 clinical trial, future clinical trials may reveal adverse events inconsistent with the safety findings observed to date. For example, in 2013, results from a Phase 3 clinical trial in PAH of imatinib (Gleevec) showed statistically significant improvement in its primary efficacy endpoint, but systemic toxicities were also observed. Although we have not observed the systemic toxicities associated with imatinib, we cannot be certain that seralutinib will not exhibit similar or other toxicities in the future as the use of seralutinib becomes more widespread if it receives regulatory approval. Many compounds that initially showed promise in early-stage testing have later been found to cause side effects that prevented further development of the compound. In addition, regulatory authorities may draw different conclusions or require additional testing to confirm these determinations. It is possible that as we test seralutinib in future clinical trials, or as the use of seralutinib becomes more widespread if it receives regulatory approval, illnesses, injuries, discomforts and other adverse events that were observed in earlier trials, as well as conditions that did not occur or went undetected in previous trials, will be reported by subjects. If such side effects become known later in development or upon approval, if any, such findings may harm our business, financial condition and prospects significantly. In addition, if seralutinib receives marketing approval, and we or others later identify undesirable side effects caused by seralutinib, a number of potentially significant negative consequences could result, including: - regulatory authorities may withdraw, suspend or limit approvals of seralutinib;- we may be required to recall a product or change the way seralutinib is administered to patients;- regulatory authorities may require additional warnings on the label, such as a "black box" warning or a contraindication;- we may be required to implement a Risk Evaluation and Mitigation Strategy, or REMS, or create a medication guide outlining the risks of such side effects for distribution to patients, or similar risk management measures;- we may be required to change the way seralutinib is distributed or administered, conduct additional clinical trials or change the labeling of seralutinib or be required to conduct additional post-marketing studies or surveillance;- we could be sued and held liable for harm caused to patients;- sales of seralutinib may decrease significantly or seralutinib could become less competitive; and - our reputation may suffer. Any of these events could prevent us from achieving or maintaining market acceptance of seralutinib, if approved, and could significantly harm our business, results of operations and prospects.

We may not be able to initiate or continue clinical trials for seralutinib if we are unable to identify and enroll a sufficient number of eligible patients to participate in these trials as may be required by the FDA or similar regulatory authorities outside the United States. Subject enrollment, a significant factor in the timing of clinical trials, is affected by many factors including the size and nature of the patient population, the proximity of patients to clinical sites, the eligibility and exclusion criteria for the trial, the design of the clinical trial, the risk that enrolled patients will not complete a clinical trial, our ability to recruit clinical trial investigators and associated staff with the appropriate competencies and experience, competing clinical trials and clinicians' and patients' perceptions as to the potential advantages and risks of the product candidate being studied in relation to other available therapies, including any new drugs that may be approved for the indications we are investigating as well as any drugs under development. We will be required to identify and enroll a sufficient number of subjects for each of our clinical trials. Potential subjects for any future clinical trials may not be adequately diagnosed or identified with the diseases which we are targeting or may not meet the entry criteria for such trials. For example, a limited number of patients are affected by PAH and other indications that we may pursue such as PH-ILD, and we have encountered difficulties enrolling patients in our previous clinical trials of seralutinib in PAH patients. We also may encounter difficulties in identifying and enrolling subjects with a stage of disease appropriate for any future trials of seralutinib and monitoring such subjects adequately during and after treatment. We may not be able to initiate or continue clinical trials if we are unable to locate a sufficient number of eligible subjects to participate in the clinical trials required by the FDA or comparable foreign regulatory authorities. In addition, the process of finding and diagnosing subjects may prove costly. The timing of our clinical trials depends, in part, on the speed at which we can recruit patients to participate in our trials, as well as completion of required follow-up periods. The eligibility criteria of our clinical trials, once established, will further limit the pool of available trial participants. For example, PAH is a rare disease with limited patient pools from which to draw. If patients are unwilling to participate in our trials for any reason, including the existence of concurrent clinical trials for similar patient populations in PAH, if they are unwilling to enroll in a clinical trial with a placebo-controlled design or the availability of approved therapies, or we otherwise have difficulty enrolling a sufficient number of patients, the timeline for recruiting subjects, conducting studies and obtaining regulatory approval of seralutinib may be delayed. Our inability to enroll a sufficient number of subjects for any of our future clinical trials would result in significant delays or may require us to abandon one or more clinical trials altogether. In addition, we expect to rely on CROs and clinical trial sites to ensure proper and timely conduct of our future clinical trials and, while we intend to enter into agreements governing their services, we will have limited influence over their actual performance. We cannot assure you that our assumptions used in determining expected clinical trial timelines are correct or that we will not experience delays in enrollment, which would result in the delay of completion of such trials beyond our expected timelines.

Before obtaining marketing approval from regulatory authorities for the sale of seralutinib, we must conduct extensive clinical studies to demonstrate the safety and efficacy of seralutinib in humans. In addition, before we can initiate clinical development for our product candidates, and in some cases, before we can pursue clinical development of a product candidate for a new potential indication, we must submit the results of preclinical studies to the FDA along with other information, including information about product candidate chemistry, manufacturing and controls and our proposed clinical trial protocol, as part of an IND, and we are also required to submit regulatory filings to foreign regulatory authorities for clinical trials outside of the United States. We do not know whether our ongoing or future trials will begin on time or be completed on schedule, if at all. The commencement, data readouts and completion of clinical trials can be delayed for a number of reasons including delays related to: - the FDA or comparable foreign regulatory authorities disagreeing as to the design or implementation of our clinical studies, including the doses and endpoints of our ongoing or potential future Phase 3 clinical trial of seralutinib;- obtaining regulatory authorizations to commence a trial or reaching a consensus with regulatory authorities on trial design;- any failure or delay in reaching an agreement with contract research organizations, or CROs, and clinical trial sites, the terms of which can be subject to extensive negotiation and may vary significantly among different CROs and trial sites;- obtaining approval or positive opinion from one or more institutional review boards, or IRBs or ethics committees;- IRBs refusing to approve, suspending or terminating a trial at an investigational site, precluding enrollment of additional subjects, or withdrawing their approval of a trial;- changes to clinical trial protocol;- clinical sites deviating from trial protocol or dropping out of a trial;- manufacturing sufficient quantities of seralutinib or obtaining sufficient quantities of combination therapies for use in clinical trials;- subjects failing to enroll or remain in our trials at the rate we expect, or failing to return for post-treatment follow-up, including subjects failing to remain in our trials;- subjects choosing an alternative treatment for PAH or other indications including PH-ILD for which we are developing seralutinib, or participating in competing clinical trials;- lack of adequate funding to continue a clinical trial;- subjects experiencing severe or unexpected drug-related adverse effects;- occurrence of serious adverse events in trials of the same class of agents conducted by other companies;- selection of clinical endpoints that require prolonged periods of clinical observation or analysis of the resulting data;- a facility manufacturing seralutinib or any of its components, including the device component of orally inhaled seralutinib, being ordered by the FDA or comparable foreign regulatory authorities to temporarily or permanently shut down due to violations of cGMP or similar foreign regulations or other applicable requirements, or infections or cross-contaminations of seralutinib in the manufacturing process;- any changes to our manufacturing process that may be necessary or desired;- third-party clinical investigators losing the licenses or permits necessary to perform our clinical trials, not performing our clinical trials on our anticipated schedule or consistent with the clinical trial protocol, good clinical practices, or GCP, or other regulatory requirements; third-party contractors not performing data collection or analysis in a timely or accurate manner; or - third-party contractors becoming debarred or suspended or otherwise penalized by the FDA or other government or regulatory authorities for violations of regulatory requirements, in which case we may need to find a substitute contractor, and we may not be able to use some or all of the data produced by such contractors in support of our marketing applications. Such delays or regulatory feedback on our trial designs could also significantly increase the costs of our clinical trials, including any future clinical trials of seralutinib. We could also encounter delays if a clinical trial is suspended or terminated by us, by the IRBs of the institutions in which such trials are being conducted, by a Data Safety Monitoring Board for such trial or by the FDA or comparable foreign regulatory authorities. Such authorities may impose such a suspension or termination due to a number of factors, including failure to conduct the clinical trial in accordance with regulatory requirements or our clinical protocols, inspection of the clinical trial operations or trial site by the FDA or comparable foreign regulatory authorities resulting in the imposition of a clinical hold, unforeseen safety issues or adverse side effects, failure to demonstrate a benefit from using a drug, changes in governmental regulations or administrative actions or lack of adequate funding to continue the clinical trial. In addition, changes in regulatory requirements and policies may occur, and we may need to amend clinical trial protocols to comply with these changes. Amendments may require us to resubmit our clinical trial protocols to IRBs or ethics committees for reexamination, which may impact the costs, timing or successful completion of a clinical trial. In addition, the FDA's and other regulatory authorities' policies with respect to clinical trials may change and additional government regulations may be enacted. For instance, the regulatory landscape related to clinical trials in the EU recently evolved. The EU Clinical Trials Regulation, or CTR, which was adopted in April 2014 and repeals the EU Clinical Trials Directive, became applicable on January 31, 2022. While the EU Clinical Trials Directive required a separate clinical trial application, or CTA, to be submitted in each member state in which the clinical trial takes place, to both the competent national health authority and an independent ethics committee, the CTR introduces a centralized process and only requires the submission of a single application concerned for multi-center trials. The CTR allows sponsors to make a single submission to both the competent authority and an ethics committee in each member state, leading to a single decision per member state. The assessment procedure of the CTA has been harmonized as well, including a joint assessment by all member states concerned, and a separate assessment by each member state with respect to specific requirements related to its own territory, including ethics rules. Each member state's decision is communicated to the sponsor via the centralized EU portal. Once the CTA is approved, clinical study development may proceed. The CTR transition period ended on January 31, 2025, and all clinical trials (and related applications) are now fully subject to the provisions of the CTR. Compliance with the CTR requirements by us and our third-party service providers, such as contract research organizations, or CROs, may impact our developments plans. The UK regulatory framework in relation to clinical trials is derived from the now-repealed EU Clinical Trials Directive (as implemented into UK law, through the Medicines for Human Use (Clinical Trials) Regulations 2004, as amended). In April 2025, the UK government introduced the Medicines for Human Use (Clinical Trials) Amendment Regulations 2024. The amendment, which will take full effect from April 2026, aims to provide a more flexible regime to make it easier to conduct clinical trials in the UK, increase the transparency of clinical trials conducted in the UK and make clinical trials more patient centered. Under the terms of the Protocol on Ireland/Northern Ireland, provisions of the (EU) CTR which relate to the manufacture and import of investigational medicinal products and auxiliary medicinal products apply in Northern Ireland. Clinical trial submissions in the UK will not be able to be bundled with those of EU member states within the EMA CTIS, adding further complexity, cost and potential risk to future clinical and development activity in the UK. If we are slow or unable to adapt to changes in existing requirements or the adoption of new requirements or policies governing clinical trials, our development plans may also be impacted. Further, conducting clinical trials in foreign countries, as we currently and may continue to do for seralutinib, presents additional risks that may delay completion of our clinical trials. These risks include the failure of enrolled patients in foreign countries to adhere to clinical protocol as a result of differences in healthcare services or cultural customs, managing additional administrative burdens associated with foreign regulatory schemes, as well as political and economic risks, including war, relevant to such foreign countries. For example, we are currently conducting the open label Phase 3 study of seralutinib in PAH at sites outside the United States. If we experience delays in the completion of, or termination of, any clinical trial of seralutinib, the commercial prospects of seralutinib will be harmed, and our ability to generate product revenues from seralutinib will be delayed. Moreover, any delays in completing our clinical trials will increase our costs, slow down development and approval process for seralutinib and jeopardize our ability to commence product sales and generate revenues. In addition, many of the factors that cause, or lead to, termination or suspension of, or a delay in the commencement or completion of, clinical trials may also ultimately lead to the denial of regulatory approval of seralutinib. We may make formulation or manufacturing changes to seralutinib, in which case we may need to conduct additional preclinical studies to bridge our modified seralutinib to an earlier version. Any delays to our clinical trials that occur as a result could shorten any period during which we may have the exclusive right to commercialize seralutinib and our competitors may be able to bring products to market before we do, and the commercial viability of seralutinib could be significantly reduced. Any of these occurrences may harm our business, financial condition and prospects significantly.

Clinical drug development is expensive and can take many years to complete, and its outcome is inherently uncertain. We cannot guarantee that any clinical trials will be conducted as planned or completed on schedule, if at all, and failure can occur at any time during the preclinical study or clinical trial process. Despite promising preclinical or clinical results, seralutinib may unexpectedly fail. The historical failure rate for product candidates in our industry is high. The results from preclinical studies or clinical trials of seralutinib or a competitor's product candidate in the same class may not predict the results of later clinical trials of seralutinib, and interim, topline or preliminary results of a clinical trial are not necessarily indicative of final results. Product candidates in later stages of clinical trials may fail to show the desired safety and efficacy characteristics despite having progressed through preclinical studies and initial clinical trials. It is not uncommon to observe results in clinical trials that are unexpected based on preclinical studies and early clinical trials, and many product candidates fail in clinical trials despite very promising early results. For example, in February 2026, we announced that the Phase 3 PROSERA clinical trial did not meet its primary endpoint . Moreover, these and any future preclinical and clinical data may be susceptible to varying interpretations and analyses. A number of companies in the pharmaceutical and biotechnology industries have suffered significant setbacks in clinical development even after achieving promising results in earlier studies. For the foregoing reasons, we cannot be certain that our ongoing and future clinical trials and preclinical studies will be successful. Any safety concerns observed in any one of our clinical trials in our targeted indications could limit the prospects for regulatory approval of seralutinib in PAH and other indications that we may pursue in the future, including PH-ILD, which could have a material adverse effect on our business, financial condition and results of operations.