Merus goes into phase 3

Nearly a year after first proposing a phase 3 trial of petosemtamab, an anti-EGFR x LGR5 bispecific, in pretreated head and neck cancer Merus is to begin this study. A newly listed clinicaltrials.gov entry reveals that the MCLA-158-CL02 trial, in 500 patients who have progressed after receiving anti-PD-1 therapy and platinum chemo, will start this month. The trial already appeared on OncologyPipeline 12 months ago, and recent results supporting its initiation include those presented at ASCO, amounting to a 62% ORR – apparently irrespective of patients’ HPV status – among 26 subjects given petosemtamab plus Keytruda in an uncontrolled phase 1/2 study. Another key piece of the plan to launch phase 3 was securing the necessary cash, and on the strength of the ASCO data Merus closed a $400m equity offering in May. However, unlike phase 1/2, the phase 3 trial won’t involve a Keytruda combo but rather petosemtamab monotherapy, and will compare this against chemo or Erbitux. The co-primary endpoints, ORR and overall survival, suggest that the company plans to use initial readout of the former metric to back petosemtamab’s accelerated approval, with subsequent OS numbers being used to convert this into a full green light.