ASCO24: Merus bispecific bolsters Keytruda in head-and-neck cancer
23 May 2024
Clinical ResultASCOPhase 1Phase 2Immunotherapy
ASCO24: Merus bispecific bolsters Keytruda in head-and-neck cancer
Merus said its experimental bispecific antibody petosemtamab (MCLA-158) has delivered encouraging early efficacy signals when combined with Merck & Co.'s immunotherapy Keytruda (pembrolizumab) in patients with advanced head and neck squamous cell carcinoma (HNSCC). The Phase II study findings were unveiled Thursday in an abstract slated for presentation at the American Society of Clinical Oncology (ASCO) meeting that kicks off later this month.
Data presented last year showed that monotherapy with petosemtamab, which targets EGFR and LGR5, achieved an overall response rate (ORR) of 37.2% in second-line HNSCC patients – a population where standard of care is not defined and where therapies and combinations have achieved ORRs "below 20%," BMO Capital Markets analysts noted ahead of ASCO's data drop.
ORR of 60%
The results unveiled Thursday are derived from data based on a November 6 cutoff. Among 26 people treated with petosemtamab plus Keytruda in the Phase II study as of that date, 10 were evaluable for response. The most frequent primary tumour locations were oropharynx, the oral cavity and hypopharynx.
Six of the 10 evaluable patients achieved tumour responses, including one confirmed complete response (CR) and two confirmed partial responses (PRs). There were also three unconfirmed PRs, of which all three were subsequently confirmed.
Prior to the readout, Needham analysts suggested a response rate in the mid-60% range would be a "reasonable" base case expectation, including a mid-60% ORR for HPV-negative patients and a low-50% ORR for HPV-positive patients.
The interim data snapshot also showed the combination was well-tolerated among the overall study population, with no significant overlapping toxicities. Treatment-related adverse events were reported across the full study cohort, but most were low-grade. Infusion-related reactions were seen in just under 27% of patients overall, with around 4% being rated as Grade 3, and Merus said all of those occurred during the first infusion and were resolved.
Potential $2.5B in sales
Results from the study will be presented at ASCO on June 3. However, the jury is still out on whether the early tumour response rates seen with petosemtamab can translate into durable clinical benefits as the combination study matures. Merus has said it intends to provide a data update for the monotherapy portion of the study in second-line patients in the second half.
Meanwhile, Needham analysts indicated that if the ASCO data support the potential for the combo to become the standard of care in first-line HNSCC, petosemtamab could generate over $2.5 billion in annual sales.
On the competitive front, the analysts noted that Merus' drug could stand out compared to Bicara Therapeutics' bifunctional EGFR/TGF-β inhibitor BCA-101 thanks to its "cleaner safety profile." Phase I data on BCA-101 plus Keytruda presented last year showed a 65% ORR in HPV-negative patients with HNSCC, including 12 confirmed PRs and one confirmed CR.
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