- Petosemtamab in combination with FOLFOX /FOLFIRI (1L and 2L mCRC) and as monotherapy (3L+ mCRC), demonstrates antitumor activity and a manageable safety profile

UTRECHT, The Netherlands and CAMBRIDGE, Mass., Oct. 14, 2025 (GLOBE NEWSWIRE) -- Merus N.V. (Nasdaq: MRUS) (Merus, the Company, we, or our), an oncology company developing innovative, full-length multispecific antibodies and antibody drug conjugates (Biclonics^®, Triclonics^® and ADClonics^®), today announced initial interim clinical data as of an April 28, 2025 data cutoff from the ongoing phase 2 trial of the bispecific antibody petosemtamab in combination with standard of care FOLFOX/FOLFIRI in 1L, 2L metastatic CRC (mCRC) and petosemtamab monotherapy in 3L+ mCRC. Updated data will be presented in a plenary session oral presentation by Dr. Moh’d Khushman M.D., Washington University School of Medicine, St. Louis, MO at the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics on Friday, October 24 at 10:20 a.m. ET.

“We are encouraged by these early data indicating the promise of petosemtamab to combine safely with chemotherapy, and its potential to benefit a wide range of cancer patients that have metastatic colorectal cancer,” said Bill Lundberg, M.D., President, Chief Executive Officer of Merus. “We look forward to providing a more mature clinical update of a larger cohort of patients from a later cutoff date in our plenary session oral presentation.”

Petosemtamab (MCLA-158: EGFR x LGR5 Biclonics^®):

Presentation title: Petosemtamab (MCLA-158) monotherapy or with chemotherapy in metastatic colorectal cancer: Preliminary antitumor activity and safety data from a phase 2 trial

Observations in the abstract include:

As of an April 28, 2025 data cutoff date:  

• 36 patients (pts) with left- and/or right-sided, KRAS, NRAS, and BRAF wildtype microsatellite stable mCRC received petosemtamab 1500 mg Q2W, in combination with FOLFOX/FOLFIRI or as monotherapy
  • Pts treated in 1L or 2L had no prior anti-EGFR therapy
  • Pts treated in 2L received 1 prior chemotherapy regimen in the metastatic setting
  • Pts treated in 3L+ received at least 2 prior regimens in the metastatic setting, including a prior anti-EGFR therapy
• 1L petosemtamab with FOLFOX/FOLFIRI
  • 7 pts were treated in 1L (6 FOLFOX and 1 FOLFIRI), with 6 ongoing
  • 3 pts were efficacy evaluable, with median follow up of 2.6 months
  • 1 unconfirmed complete response and 2 partial responses (PR; 1 unconfirmed) observed
• 2L petosemtamab with FOLFOX/FOLFIRI
  • 10 pts were treated in 2L (1 FOLFOX and 9 FOLFIRI), with 8 ongoing
  • 8 were efficacy evaluable, with median follow up of 3.4 months
  • 4 PRs (2 unconfirmed), 3 stable diseases (SD; all ongoing) and 1 clinical deterioration prior to first scan
• All unconfirmed responses in 1L and 2L were continuing on therapy without disease progression
• 3L+ petosemtamab monotherapy:
  • 19 pts were treated, with 12 pts ongoing
  • 14 were efficacy evaluable, with median follow up 2.5 months,
  • 1 unconfirmed PR ongoing without disease progression, 6 SDs (all ongoing), 6 progressive diseases and 1 death unrelated to treatment prior to first scan observed
• Petosemtamab safety:
  • No fatal treatment-related TEAEs observed in each cohort
  • Petosemtamab plus FOLFOX:
    • Most frequent treatment-emergent adverse events (TEAEs) regardless of causality (all Grades [G]/G3) were dermatitis acneiform (71%/0%), constipation (43%/0%), fatigue (43%/0%), and peripheral neuropathy (43%/0%)
  • Petosemtamab plus FOLFIRI:
    • Most frequent TEAEs regardless of causality (all G/G3) were diarrhea (70%/0%), mucosal inflammation (50%/10%), and fatigue (40%/0%)
  • Petosemtamab monotherapy:
    • Most frequent TEAEs regardless of causality (all G/G3) were rash (58%/0%), and nausea (26%/0%)  
      

Presentations: 
Title: Petosemtamab (MCLA-158) monotherapy or with chemotherapy in metastatic colorectal cancer: Preliminary antitumor activity and safety data from a phase 2 trial 
Session Title: Plenary Session 4: Clinical Trials Plenary Session 
Date and Time: Friday, October 24, 10:20 a.m. ET 
The same data will also be available in a poster: 
Session Title: Poster Session B 
Session Date and Time: Friday, October 24, 12:30-4:00 p.m. ET The full presentations are planned to be available on the Merus website at the start of each session.

About Merus N.V.  
Merus is an 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 and LinkedIn.

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 these early data and our belief that it indicates the promise of petosemtamab to combine safely with chemotherapy, and its potential to benefit a wide range of cancer patients that have metastatic colorectal cancer; our looking forward to providing a more mature clinical update of a larger cohort of patients from a later cutoff date in our plenary session oral presentation; the clinical development of our clinical candidates, including petosemtamab, future clinical trial results or interim data, clinical activity and safety profile, and development plans in the on-going trials and described in forthcoming posters or presentations. 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 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 volatility in the global economy, including global instability, including the ongoing conflicts in Europe and the Middle East; 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, 2025, filed with the Securities and Exchange Commission, or SEC, on August 5, 2025, 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^®, Triclonics^®, and ADClonics^® are registered trademarks of Merus N.V. 

Investor and Media Inquiries:  
Sherri Spear 
Merus N.V. 
SVP Investor Relations and Strategic Communications
617-821-3246 
s.spear@merus.nl 

Kathleen Farren  
Merus N.V. 
Director Investor Relations and Corporate Communications 
617-230-4165 
k.farren@merus.nl 

Source: Merus N.V.