Thursday, Merus N.V. (NASDAQ:MRUS) announced the publication of an abstract regarding petosemtamab in combination with pembrolizumab on the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting website.

Keytruda (pembrolizumab) is Merck & Co Inc's (NYSE:MRK) top selling cancer drug.

The abstract presents interim clinical data from a cohort of 26 patients enrolled as of the abstract cutoff date, evaluating the combination in first-line (1L) recurrent/metastatic (r/m) head and neck squamous cell carcinoma (HNSCC).

As of a November 6, 2023, data cutoff date:

• Ten patients were evaluable for response, and six responses were observed. This included 1 confirmed complete response, 2 confirmed partial responses, and three unconfirmed partial responses (2 confirmed as of the abstract submission and the 3rd also subsequently confirmed).
• The combination was well tolerated, and no significant overlapping toxicities were observed.
• Treatment-emergent adverse events were reported in all patients; most were Grade 1 or 2 in severity.
• Infusion-related reactions (composite term) were reported in 26.9% (all Grades), of which 3.8% were Grade 3. All occurred during the first infusion and were resolved.

The poster concluded that petosemtamab, in combination with pembrolizumab, demonstrates a well-tolerated safety profile and promising preliminary clinical efficacy.

William Blair writes that overall, the abstract disclosed a response rate of 60% in 10 patients. While this is clearly an early dataset, and we expect at least 26 patients evaluable in the full ASCO presentation, we are highly encouraged to see this level of efficacy, including a complete responder.

"Overall, this does appear to meet the bar set by many investors going into the release of a 60% response rate, and importantly the press release notes the response rate has further improved."

The analyst reaffirms the Outperform rating.

Price Action: MRUS shares are up 32.80% at $58.41 at the last check on Friday.