<img src="https://ml.globenewswire.com/Resource/Download/b8470129-5d30-4368-8074-d77404b65be8?size=2" nborder="0" align="left" hspace="5" vspace="5" title="Compass-logo-RGB-outlines.png" alt="Compass Therapeutics"/><ul type="disc"><li style="margin-bottom:12pt;">CTX-8371, a novel dual checkpoint blocker that simultaneously targets the programmed death receptor PD-1 and its ligand PD-L1, demonstrated promising monotherapy clinical activity in patients with advanced malignancies resistant to prior immune checkpoint inhibitors.</li><li style="margin-bottom:12pt;">Deep and durable responses were observed in patients with triple-negative breast cancer (TNBC), Hodgkin lymphoma (HL), and non-small cell lung cancer (NSCLC).</li><li style="margin-bottom:12pt;">CTX-8371 was generally well tolerated with no observed dose limiting toxicities (DLTs). </li></ul> BOSTON, May 21, 2026 (GLOBE NEWSWIRE) -- Compass Therapeutics, Inc. (Nasdaq: CMPX), a clinical-stage, oncology-focused biopharmaceutical company developing proprietary antibody-based therapeutics to treat multiple human diseases, today announced a poster presentation of data from the Phase 1 study of CTX-8371, a novel PD-1×PD-L1 bispecific antibody, in patients with advanced malignancies treated in the post-checkpoint inhibitor setting will be presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, taking place May 29 – June 2, 2026, in Chicago, IL. “We are pleased to share the initial clinical data from the dose escalation portion of our ongoing Phase 1 study of CTX-8371 in patients with advanced malignancies treated in the post-checkpoint inhibitor setting at ASCO,” said Thomas Schuetz, MD, PhD, CEO of Compass and Vice Chairman of the Board of Directors. “Based on the deep, confirmed, and durable responses observed in patients with NSCLC, TNBC and HL, as well as the favorable safety profile, we have initiated cohort expansions in patients with these three malignancies and anticipate reporting additional data in the fourth quarter of 2026.” Details of the presentation are as follows: Title: Phase 1 Dose Escalation of CTX-8371, a novel PD-1×PD-L1 bispecific antibody, in patients with advanced malignancies post checkpoint inhibition Presenter: Judy S Wang, MD; Florida Cancer Specialists/Sarah Cannon Research Institute- Sarasota, Sarasota, FL Date &amp; Time: May 30, 2026 at 1:30-4:30 pm CT Session: Developmental Therapeutics—Immunotherapy Abstract number: 2629 Poster Board: 419 Location: McCormick Place Convention Center, Hall A   Data highlights from the poster presentation include: <ul type="disc"><li style="margin-bottom:12pt;">15 patients completed the dose-limiting toxicity (DLT) evaluation period and had at least one post-baseline disease assessment in the dose escalation cohort of the Phase 1, open-label, first-in-human study evaluating CTX-8371 in patients with metastatic or locally advanced malignancies.</li><li style="margin-bottom:12pt;">There were three responses: one patient with TNBC achieved &gt; 90% reduction in target tumor lesions, one patient with HL achieved a partial metabolic response, and one patient with NSCLC achieved complete resolution of target lesions after initial pseudo-progression.</li><li style="margin-bottom:12pt;">At the two highest dose levels (3.0 and 10.0 mg/kg), the overall response rate (ORR) was 33% (2 of 6 evaluable patients). The responses at the two highest dose levels were significantly durable: 10.5+ months for TNBC and 7.5+ months HL. Both of these patients remain on study with continuing durability.</li><li style="margin-bottom:12pt;">CTX-8371 was well tolerated with no DLTs. All treatment-related adverse events (AEs) were mild Grade 1 or Grade 2, with the exception of one asymptomatic Grade 3 lipase increase.</li></ul> A copy of the presentation materials can be accessed on the Compass website at <a href="https://www.globenewswire.com/Tracker?data=nZzdbzTS673_xwTWPRAQEO73V5gfeSXi6t4KKbUGqSqqcq9NKgAREw55V7z_9hByIbX_AUC2gWEg7pp8QHj4HBI_JMkqLPLL0N0WGJlCICQLa9gpiwpFcusJkKoISjp-TaJWY5bCxiu2SGVURNdJ3xnZzUe-0CR-WBnzp3Po8uE=" rel="nofollow" target="_blank" title="">https://www.compasstherapeutics.com/pipeline</a> once the presentation has concluded. About Compass Therapeutics Compass Therapeutics, Inc. was founded in 2014 and is headquartered in Boston, MA. Compass is a clinical-stage, oncology-focused biopharmaceutical company discovering and developing proprietary antibody-based therapeutics to treat multiple diseases. The company’s scientific focus is on the relationship between angiogenesis, the immune system and tumor growth. Compass has a robust pipeline of novel product candidates designed to target multiple key biological pathways to drive an effective anti-tumor response, including angiogenesis modulation, immune activation within the tumor microenvironment, and reduction of tumor-driven immunosuppression. The company is advancing discovery candidates through clinical development to commercial-stage assets. For more information, visit <a href="https://www.globenewswire.com/Tracker?data=oo6npsOjMJc80UYvpxKbFrTISisDqYfpRNxW-WgaBT398ydq4gb6L2tD8eakVSr5zhpzSvhO4ReuzHeG_B-7GyMhXSWUmWdr5Fu3DP3zFbWpAiCbBvHy-wPQdkhXqaSO" rel="nofollow" target="_blank" title="www.compasstherapeutics.com">www.compasstherapeutics.com</a>. Forward-Looking Statements This press release contains forward-looking statements. Statements in this press release that are not purely historical are forward-looking statements. Such forward-looking statements include, among other things, references to Compass’s financial position to continue advancing its product candidates, expectations about cash runway, business and development plans, and statements regarding Compass’s product candidates, including their development and clinical trial milestones such as the expected trial design, timing of enrollment, patient dosing and data readouts, regulatory plans with respect to Compass’s product candidates and the therapeutic potential thereof. Actual results could differ from those projected in any forward-looking statements due to numerous factors. Such factors include, among others, Compass’s ability to raise the additional funding it will need to continue to pursue its business and product development plans, the inherent uncertainties associated with developing product candidates and operating as a development stage company, Compass’s ability to identify additional product candidates for development, Compass’s ability to develop, complete clinical trials for, obtain approvals for and commercialize any of its product candidates, competition in the industry in which Compass operates and market conditions. These forward-looking statements are made as of the date of this press release, and Compass assumes no obligation to update the forward-looking statements, or to update the reasons why actual results could differ from those projected in the forward-looking statements, except as required by law. Investors should consult all of the information set forth herein and should also refer to the risk factor disclosure set forth in the reports and other documents Compass files with the U.S. Securities and Exchange Commission (SEC) available at www.sec.gov, including without limitation Compass’s latest Annual Report on Form 10-K, Quarterly Report on Form 10-Q and subsequent filings with the SEC. Investor Contact <a href="https://www.globenewswire.com/Tracker?data=Ox3LjNMtFVqn73qxjz9b7sBXS__o6ZGgCb725gAoJlTHf5ISqx3ZL3PieiHSIXP34iPYuUp8H09J9a4n8oVfvqyVNPo-Ifzlrp-3O7JuY6x3LUKsr5T0L3eddRvFR3FW" rel="nofollow" target="_blank" title="ir@compasstherapeutics.com">ir@compasstherapeutics.com</a>  Media Contact Anna Gifford, Chief of Staff <a href="https://www.globenewswire.com/Tracker?data=JR3vrw_aldr5Jz-rAH8QrFkItOBxapGKmGQWrkvmADIZCwnI9RN3Ba_ELEXY6NNBruXuR-HtnJMbTksr2fp8HWDDnjF6CK3-KASIuCL6YYIpzeCkX5F9WGHoCIZM3Qfq" rel="nofollow" target="_blank" title="media@compasstherapeutics.com">media@compasstherapeutics.com</a>  617-500-8099  <img alt="" src='https://ml.globenewswire.com/media/Nzk3YjVkYTUtMTNjOS00NzcyLWFlNTItNDU2MjkwYTY5OGMyLTEyMTM5NzUtMjAyNi0wNS0yMS1lbg==/tiny/Compass-Therapeutics.png' referrerpolicy='no-referrer-when-downgrade' />

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Compass Therapeutics to Present Promising Phase 1 Clinical Data for CTX-8371 in Patients with Advanced Malignancies Treated in the Post-Checkpoint Inhibitor Setting at the 2026 ASCO Annual Meeting

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