<img src="https://ml.globenewswire.com/Resource/Download/de376a45-7a16-49db-8ad4-65ff45472c90?size=2" nborder="0" align="left" hspace="5" vspace="5" title="Zymeworks Logo_color.png" alt="Zymeworks Inc."/><ul type="disc"><li style="margin-bottom:8pt;">ZW191 demonstrates compelling anti-tumor activity in platinum-resistant ovarian cancer patients regardless of FRα expression level</li><li style="margin-bottom:8pt;">Confirmed objective response rate (cORR) of 78.6% in FRα-positive (≥75% at PS2+) platinum-resistant ovarian cancer patients and 47.4% in FRα-negative patients (&lt;75% at PS2+) across all dose levels studied</li><li style="margin-bottom:8pt;">Median duration of response was not reached at the time of data cutoff, and median progression-free survival was 7.6 months across ovarian and endometrial cancer cohorts</li><li style="margin-bottom:8pt;">Patient recruitment in dose optimization cohorts completed, with favorable tolerability profile and broad therapeutic window supporting continued clinical development</li></ul> VANCOUVER, British Columbia, June 14, 2026 (GLOBE NEWSWIRE) -- Zymeworks Inc. (Nasdaq: ZYME), a biotechnology company managing a portfolio of licensed healthcare assets while developing a diverse pipeline of novel, multifunctional biotherapeutics, today presented new clinical data from the dose-escalation portion of its ongoing Phase 1 study evaluating ZW191, a folate receptor alpha (FRα)-targeting antibody-drug conjugate (ADC), at the European Society for Medical Oncology (ESMO) Gynaecological Cancers Congress 2026. The presentation highlights compelling anti-tumor activity in patients with platinum-resistant ovarian cancer (PROC) and in patients with endometrial cancer, including patients with both positive and negative FRα expression. The results further support the potential of ZW191 to address limitations of currently available and investigational FRα-targeted therapies and broaden treatment opportunities for patients with gynecologic cancers. “We are highly encouraged by these data, which continue to demonstrate the differentiated profile of ZW191 and its potential to deliver meaningful clinical benefit across a broad population of patients with ovarian and endometrial cancers,” said Sabeen Mekan, M.D., Senior Vice President and Chief Medical Officer of Zymeworks. “The response rate observed in FRα-positive ovarian cancer patients compares favorably with currently available therapies, while maintaining meaningful activity in patients with negative FRα expression. Together these encouraging data on durability, progression-free survival, and manageable safety profile further strengthen our confidence in the program and reinforce the ability of our ADC platform to generate differentiated therapeutics.” The analysis included efficacy data by FRα expression level from Part 1 of the ongoing Phase 1 study as of the March 9, 2026, data cutoff. FRα expression was assessed by immunohistochemistry and categorized using the Proportion and Staining Intensity, defined as the percentage of cells with 2+/3+ staining. Tumors were categorized as FRα-negative (&lt;75%) or FRα-positive (≥75%). Key Findings Among response-evaluable PROC patients, ZW191 demonstrated a cORR of 78.6% in patients with FRα-positive tumors and 47.4% in patients with FRα-negative tumors across all dose levels. Disease control rates were 100.0% and 89.5%, respectively. Confirmed ORR in the overall PROC population was 58.8% across all dose levels studied and 65.2% in dose range of 6.4-9.6 mg/kg. These findings demonstrate meaningful anti-tumor activity across both FRα-positive and FRα-negative tumors as well as in the overall population. In endometrial cancer patients with FRα-negative tumors, ZW191 demonstrated a cORR of 40.0% and a disease control rate of 80.0% across all doses evaluated. Across both ovarian and endometrial cancer cohorts, responses were observed early and continued to deepen over time. Median duration of response was not reached at the time of data cutoff, and median progression-free survival was 7.6 months. ZW191 continued to demonstrate a favorable tolerability profile. Treatment-emergent adverse events (TEAEs) occurred in 98% of patients, with grade ≥3 TEAEs reported in 55% of patients. The most common grade ≥3 adverse events were neutropenia (24%), anemia (20%), and thrombocytopenia (12%). Serious TEAEs occurred in 35% of patients, and 20% of patients discontinued treatment due to adverse events. Overall, the safety profile was manageable and consistent with continued clinical development. “These results further demonstrate the potential of ZW191 to provide meaningful clinical benefit for patients with difficult-to-treat gynecologic cancers,” said Kosei Hasegawa, M.D., Ph.D., Saitama Medical University International Medical Center and presenting author. “The robust activity observed in FRα-positive ovarian cancer, together with encouraging responses in tumors with lower FRα expression, suggests ZW191 could expand the benefit of FRα-targeted therapy to a broader patient population.” Part 2a, the dose optimization portion of the Phase 1 study evaluating ZW191 in ~60 PROC patients randomized to either 6.4 mg/kg every three weeks or 9.6 mg/kg every three weeks, has completed enrollment. Data from Part 2a will be presented at a future medical meeting and are expected to inform dose selection for potential future development. ZW191’s differentiated profile, including its novel FRα-targeting antibody, ZD06519 payload, and high drug-to-antibody ratio, supports its potential to address key limitations of current therapies and broaden the applicability of FRα-targeted treatment approaches across multiple tumor types. About ZW191 ZW191 is an antibody-drug conjugate engineered to target a protein called folate receptor-⍺ found in ~75% of high-grade serous ovarian carcinomas1, over 50% of endometrial cancers2,3 and ~70% of lung adenocarcinomas4. ZW191’s differentiated design strongly supports its ability to internalize into FR⍺-expressing cells with the potential to release bystander active topoisomerase-1 inhibitor (ZD06519), a novel proprietary payload developed by Zymeworks to kill tumor cells. About Zymeworks Inc.  Zymeworks is a global biotechnology company managing a portfolio of licensed healthcare assets and developing a diverse pipeline of novel, multifunctional biotherapeutics to improve the standard of care for difficult-to-treat diseases, including cancer, inflammation, and autoimmune disease. Zymeworks’ asset and royalty aggregation strategy focuses on optimizing positive future cash flows from an emerging portfolio of licensed products such as Ziihera® (zanidatamab-hrii) and other licensed products and product candidates, such as pasritamig. In addition, Zymeworks is also building a portfolio of healthcare assets that can generate strong cash flows, while supporting the development of innovative medicines. Zymeworks engineered and developed Ziihera, a HER2-targeted bispecific antibody using Zymeworks’ proprietary Azymetric™ technology and has entered into separate agreements with BeOne Medicines Ltd. (formerly BeiGene, Ltd.) and Jazz Pharmaceuticals Ireland Limited granting each exclusive rights to develop and commercialize zanidatamab in different territories. Zymeworks is rapidly advancing a robust pipeline of product candidates, leveraging its expertise in both antibody drug conjugates and multispecific antibody therapeutics targeting novel pathways in areas of significant unmet medical need. Zymeworks’ complementary therapeutic platforms and fully integrated drug development engine provide the flexibility and compatibility to precisely engineer and develop highly differentiated antibody-based therapeutics. These capabilities have been further leveraged through strategic partnerships with global biopharmaceutical companies. For information about Zymeworks, visit <a href="https://www.globenewswire.com/Tracker?data=PbBRm1jx1fB1CCEZ7RxXZx3Jw1a1s2iRYakMhafXzQiMI1IplmP2SFYRb06rU5gkFZ3uiZNKHgPHz_c2XmL1Tg0bEfdeRRDXq2PBOFavwlQ=" rel="nofollow" target="_blank" title="www.zymeworks.com">www.zymeworks.com</a> and follow @ZymeworksInc on X. Cautionary Note Regarding Forward-Looking Statements This press release includes “forward-looking statements” or information within the meaning of the applicable securities legislation, including Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. Forward-looking statements in this press release include, but are not limited to, statements that relate to the potential safety profile and therapeutic effects of ZW191; Zymeworks’ development of product candidates; status of studies and the related data; anticipated clinical data presentations; Zymeworks’ implementation of its long-term strategy; and other information that is not historical information. When used herein, words such as “plan”, “believe”, “expect”, “may”, “continue”, “anticipate”, “potential”, “will”, “on track”, “progress”, “preserve”, “intend”, “could”, and similar expressions are intended to identify forward-looking statements. In addition, any statements or information that refer to expectations, beliefs, plans, projections, objectives, performance or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking. All forward-looking statements are based upon Zymeworks’ current expectations and various assumptions. Zymeworks believes there is a reasonable basis for its expectations and beliefs, but they are inherently uncertain. Zymeworks may not realize its expectations, and its beliefs may not prove correct. Actual results could differ materially from those described or implied by such forward-looking statements as a result of various factors, including, without limitation: any of Zymeworks’ or its partners’ product candidates, including ZW191, may fail in development, may not receive required regulatory approvals, or may be delayed to a point where they are not commercially viable; Zymeworks may not achieve milestones or receive additional payments or royalties under its collaborations; regulatory agencies may impose additional requirements or delay the initiation of clinical trials; the impact of new or changing laws and regulations; market conditions, including the impact of tariffs; potential negative impacts of FDA regulatory delays and uncertainty around recent policy developments, changes in the leadership of federal agencies such as the FDA, staff layoffs, budget cuts to agency programs and research, and changes in drug pricing controls; the impact of global and regional geopolitical or public health developments on Zymeworks’ business, research and clinical development plans and timelines and results of operations, including impact on its clinical trial sites, collaborators, and contractors who act for or on Zymeworks’ behalf; zanidatamab may not be successfully commercialized; Zymeworks’ business strategy related to anticipated and potential future milestones and royalty streams and existing and potential new partnerships may not be successfully implemented; Zymeworks’ evolution of its business strategy may not deliver meaningful shareholder returns; Zymeworks may be unsuccessful in actively managing and/or aggregating revenue generating assets alongside its active R&amp;D operations; ongoing and future clinical trials may not demonstrate safety and efficacy of any of Zymeworks’ or its collaborators’ product candidates, including ZW191; Zymeworks’ assumptions and estimates regarding its financial condition, future financial performance and estimated cash runway may be incorrect; inability to maintain or enter into new partnerships or strategic collaborations; and the factors described under “Risk Factors” in Zymeworks’ quarterly and annual reports filed with the Securities and Exchange Commission (copies of which may be obtained at www.sec.gov and www.sedarplus.ca). Although Zymeworks believes that such forward-looking statements are reasonable, there can be no assurance they will prove to be correct. Investors should not place undue reliance on forward-looking statements. The above assumptions, risks and uncertainties are not exhaustive. Forward-looking statements are made as of the date hereof and, except as may be required by law, Zymeworks undertakes no obligation to update, republish, or revise any forward-looking statements to reflect new information, future events or circumstances, or to reflect the occurrences of unanticipated events. Contacts: Investor Inquiries: Shrinal Inamdar Vice President, Investor Relations (604) 678-1388 <a href="https://www.globenewswire.com/Tracker?data=YyzlHneXJPjOxa7K_-DqQqaPtO8f5wsoNViA-1PFPFHaC2QCwTm5oLPURJc5VDlistk_ZfpPQ918XvfpfBBKgfGVfI7g3IVfviai-lBWO3oStorPIZNVtGxPRPY_xEA2uaToahKv262HyNQWzkjFZdYe4JSbqf1AN9mN6wxwOWNikBZ3UUg_hecnVsO-mL_jyxYgZgwTdVAW49VR4aau0DOXgGkXEjLWUuG038KbWaQRmnvbZQ0n8crRShXghv-mMMGHKcxQ3T4JEYLPRfYPqQ==" rel="nofollow" target="_blank" title="ir@zymeworks.com">ir@zymeworks.com</a>    Media Inquiries: Diana Papove Vice President, Corporate Communications (604) 678-1388 <a href="https://www.globenewswire.com/Tracker?data=8pyo7BnwP_lI5NduxEyT9tdeSvn5-zn8TFCFSKcydsPVDsjn20kv0zKCA3Do3jww4S6x7CawdY7uR8DxgT9gVjPplg5aNthN0aqCHWjn85VvgQuXjBAPaSFOD3Nzxyg0csr-c8n0dOGk5xrFbj4pUhxyxodIKNMeyR_YezlFSetkVW9QoLWMzSYFa7pZAAj2iC4LxqwkZnZJnJu1zjkoMaIFaMxcyCaQnzMX1x-7uGGn6AAxItxGMXnID2Si5E1WnqezbxnXFRX6v8Z-cqAt-g==" rel="nofollow" target="_blank" title="media@zymeworks.com">media@zymeworks.com</a> --- 1 Köbel, M., Madore, J., Ramus, S. et al., Br J Cancer 111, 2297–2307 (2014). 2 May B, Conway N, Truong T, Linhart S, et al. FRα, B7-H4, &amp; HER2 Expression in Endometrial Cancer: Assessing the Promise of Antibody Drug Conjugate Therapies. Presented at: SGO 2025 Winter Meeting; January 30 - February 1, 2025; Whistler, British Columbia, Canada. 3 Senol S, Ceyran AB, Aydin A, Zemheri E, Ozkanli S, Kösemetin D, Sehitoglu I, Akalin I. Folate receptor α expression and significance in endometrioid endometrium carcinoma and endometrial hyperplasia. Int J Clin Exp Pathol. 2015 May 1;8(5):5633-41. 4 O'Shannessy DJ, et al., Oncotarget. 2012 Apr; 3(4):414-25. <img alt="" src='https://ml.globenewswire.com/media/YWY1YWQ2YTYtMDRkNS00N2M4LThhMTItY2RhMzBhYzk1M2JiLTEyNjg0NDItMjAyNi0wNi0xNC1lbg==/tiny/Zymeworks-Inc-.png' referrerpolicy='no-referrer-when-downgrade' />

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Zymeworks Presents New Phase 1 Data for Folate Receptor Alpha-Targeting ADC ZW191 at ESMO Gynaecological Cancers Congress 2026

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