Sep 30, 2021

Title: Zenocutuzumab is an effective HER2/HER3 Biclonics® antibody in cancers with NRG1 fusions Authors: Jan Gerlach, Igor Odintsov, Alexandre Deshiere, Ron Schackmann, Marc Ladanyi, Jeroen Lammerts van Bueren, Romel Somwar, Cecile Geuijen Virtual Poster #: P201 MCLA-158 (petosemtamab) Title: Preliminary antitumor activity of MCLA-158, an IgG1 bispecific antibody targeting EGFR and LGR5, in advanced head and neck squamous cell carcinoma Authors: Antoine Hollebecque, Irene Brana, Lara Iglesias, Caroline Even, Shumei Kato, Marc Díez García, Mateo Bover, Patricia Martin-Romano, Rocio Garcia-Carbonero, Guillen Argilés, Josep Tabernero, Rajan Khanna, Viktoriya Stalbovskaya, Jeroen Lammerts van Bueren, Kees Bol, Mohamed Bekkrada, Andrew Joe, Ernesto Wasserman, Ezra E.W. Cohen Virtual Poster #: P185 The posters will be available starting Thursday, October 7 at 9:00 am ET and on-demand throughout the conference on the AACR website . The posters will also be available on the Merus website . About Zeno Zeno is an antibody-dependent cell-mediated cytotoxicity (ADCC)-enhanced Biclonics® that utilizes the Merus Dock & Block® mechanism to inhibit the neuregulin/HER3 tumor-signaling pathway in solid tumors with NRG1 gene fusions (NRG1+). Through its unique mechanism of binding to HER2 and potently blocking the interaction of HER3 with its ligand NRG1 or NRG1-fusion proteins, Zeno has the potential to be particularly effective against NRG1+ cancers. In preclinical studies, Zeno also potently inhibits HER2/HER3 heterodimer formation and tumor growth in models harboring NRG1 fusions. About MCLA-158 MCLA-158 , or petosemtamab, is an ADCC enhanced human IgG1 Biclonics® designed to bind to cancer stem cells (CSCs) expressing leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) and epidermal growth factor receptor (EGFR). In preclinical models, MCLA-158 binding triggers EGFR degradation in LGR5+ CSCs and is designed to have two different mechanisms of action. The first entails blocking of growth and survival pathways in cancer initiating cells. The second exploits the recruitment and enhancement of immune effector cells to directly kill cancer initiating cells that persist in solid tumors and can cause relapse and metastasis. About Merus N.V. Merus is a clinical-stage oncology company developing innovative full-length human bispecific and trispecific antibody therapeutics, referred to as Multiclonics®. Multiclonics® are manufactured using industry standard processes and have been observed in preclinical and clinical studies to have several of the same features of conventional human monoclonal antibodies, such as long half-life and low immunogenicity. For additional information, please visit Merus’ website, http://www.merus.nl and https://twitter.com/MerusNV . Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation statements regarding zenocutuzumab and MCLA-158’s mechanisms of action and potential of these Biclonics® in preclinical or clinical development to treat cancer. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: our need for additional funding, which may not be available and which may require us to restrict our operations or require us to relinquish rights to our technologies or Biclonics®, Triclonics® and multispecific antibody candidates; potential delays in regulatory approval, which would impact our ability to commercialize our product candidates and affect our ability to generate revenue; the lengthy and expensive process of clinical drug development, which has an uncertain outcome; the unpredictable nature of our early stage development efforts for marketable drugs; potential delays in enrollment of patients, which could affect the receipt of necessary regulatory approvals; our reliance on third parties to conduct our clinical trials and the potential for those third parties to not perform satisfactorily; impacts of the COVID-19 pandemic; we may not identify suitable Biclonics® or bispecific antibody candidates under our collaborations or our collaborators may fail to perform adequately under our collaborations; our reliance on third parties to manufacture our product candidates, which may delay, prevent or impair our development and commercialization efforts; protection of our proprietary technology; our patents may be found invalid, unenforceable, circumvented by competitors and our patent applications may be found not to comply with the rules and regulations of patentability; we may fail to prevail in potential lawsuits for infringement of third-party intellectual property; and our registered or unregistered trademarks or trade names may be challenged, infringed, circumvented or declared generic or determined to be infringing on other marks. These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10-Q for the period ended June 30, 2021 filed with the Securities and Exchange Commission, or SEC, on August 5, 2021, and our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change, except as required under applicable law. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. Multiclonics®, Biclonics® and Triclonics® are a registered trademarks of Merus N.V.