Petosemtamab has demonstrated efficacy in patients with advanced head and neck squamous cell carcinoma (HNSCC), according to research presented at the AACR Annual Meeting 2023.

“We observed clinically meaningful activity and durable responses in this cohort of patients with advanced and quite refractory head and neck squamous cell carcinoma who had been previously treated with both immunotherapy and platinum-based chemotherapy,” said study presenter Ezra E.W. Cohen, MD, of UC San Diego Health in California. 

Dr Cohen explained that petosemtamab is a bispecific antibody targeting both EGFR and LGR5. Studies have shown LGR5 expression in 52% to 89% of HNSCC tumors and EGFR expression in up to 90%. 

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Dr Cohen and colleagues evaluated petosemtamab in a phase 1/2 study ( Identifier: NCT03526835). In the phase 1 portion, patients received petosemtamab at doses ranging from 90 mg to 1500 mg every 2 weeks. The recommended phase 2 dose was 1500 mg. 

Dr Cohen reported data on 49 patients with advanced HNSCC who received petosemtamab at 1500 mg every 2 weeks until disease progression or toxicity. At baseline, the patients’ median age was 63 (range, 31-77) years, and 78% were men. They had received a median of 2 prior lines of therapy (range, 1-4). 

Forty-three patients were evaluable for efficacy. At the data cutoff, 12 of these patients (28%) were still receiving petosemtamab.

The objective response rate was 37.2%, and the disease control rate was 72.1%. One patient had a complete response, 15 had a partial response, and 15 had stable disease. 

The median time to response was 1.8 months, and the median duration of response was 6.0 months. The median progression-free survival was 5.3 months, and the median overall survival was 11.5 months.

The safety analysis included 80 patients who received the recommended phase 2 dose of petosemtamab. All patients experienced at least 1 adverse event (AE) deemed possibly related to treatment. 

The most common AEs potentially related to petosemtamab were rash (36%), hypotension (25%), and dermatitis acneiform (25%). No fatal treatment-related AEs were reported. 

Dr Cohen concluded that petosemtamab “is relatively well tolerated, with a manageable safety profile.” He added that development of petosemtamab in HNSCC is ongoing.

Disclosures: This research was supported by Merus N.V. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures. 


Cohen EEW, Fayette J, Daste A, et al. Clinical activity of MCLA-158 (petosemtamab), an IgG1 bispecific antibody targeting EGFR and LGR5, in advanced head and neck squamous cell carcinoma (HNSCC). AACR 2023. April 14-19, 2023. Abstract CT012.