On October 14, 2025 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), reported 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 (Free AACR Whitepaper)-NCI-EORTC AACR-NCI-EORTC (Free AACR-NCI-EORTC Whitepaper) International Conference on Molecular Targets and Cancer Therapeutics (EORTC-NCI-AACR) (Free ASGCT Whitepaper) (Free EORTC-NCI-AACR Whitepaper) on Friday, October 24 at 10:20 a.m. ET.

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"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.

(Press release, Merus, OCT 14, 2025, View Source [SID1234656650])