Merus (MRUS) Investor Update summary

Clinical Data and Efficacy Update

• Petosemtamab monotherapy in second-line plus recurrent/metastatic head and neck cancer (HNSCC) achieved a confirmed overall response rate of 36%, median progression-free survival of 4.9–5.2 months, and median overall survival of 11.4–12.5 months, with four complete responses among 27 responders; median duration of response was 6.2–6.7 months, with some responses ongoing for over 3 years.

• Efficacy compares favorably to historical EGFR-based therapies and supports FDA Breakthrough Therapy Designation.

• Responses were observed in both HPV-positive and negative subgroups, with evidence of deepening responses over time.

• Combination with pembrolizumab in PD-L1 positive disease showed a 67% response rate in interim data.

• Lower dose (1100 mg Q2W) cohort showed a 19% ORR, including 2 complete responses.

Safety and Tolerability

• Petosemtamab demonstrated a manageable and well-tolerated safety profile at the recommended Phase III dose of 1,500 mg biweekly, with most adverse events occurring during the first infusion.

• Updated administration regimen reduced Grade 3 infusion-related reactions from 24% to 9%.

• Skin and gastrointestinal toxicities were less frequent and severe than with other EGFR-directed antibodies; most common adverse events included dermatitis acneiform, decreased magnesium, and rash.

• No new safety signals identified; no positive exposure-safety relationship for grade ≥3 TEAEs.

Clinical Development and Regulatory Progress

• Two ongoing Phase III trials in HNSCC (LiGeR-HN1 and LiGeR-HN2) and multiple Phase II exploratory cohorts in colorectal cancer (mCRC) are underway, with additional trials planned for 2025.

• FDA accepted the 1,500 mg dose as the recommended Phase III dose following a successful Type D meeting.

• Petosemtamab received FDA Breakthrough Therapy Designation for r/m HNSCC post-platinum and anti-PD-1/PD-L1 therapy.

• Ambitious goals set for 2025 include substantial enrollment of Phase III trials and interim data readouts for colorectal cancer.