Moderna and Merck shares fall after melanoma-vaccine results emerge early

An estimated 82.2% of patients given the personalised mRNA treatment intismeran alongside pembrolizumab were alive without their melanoma returning after two years, compared with 70.0% of those given pembrolizumab and a placebo, according to results announced by drugmakers Merck and Moderna. The 12.2 percentage-point difference is a promising result for a treatment designed to stop cancer coming back after surgery.

The randomised, double-blind phase 3 trial enrolled 1,137 adults whose high-risk melanoma had been completely removed. All were assigned to receive pembrolizumab, an established immunotherapy sold as Keytruda. Of those, 757 were assigned to receive intismeran as well, while 380 were assigned a placebo.

Intismeran is made using information from each patient’s tumour. It aims to train the immune system to recognise features of that cancer if it returns. It is a treatment after surgery, not a vaccine to prevent someone developing melanoma in the first place.

After a median follow-up of 24.6 months, the companies reported a 42% lower *hazard* of melanoma returning or death from any cause in the combination group. That figure measures a combined outcome over the follow-up period; it does not mean the vaccine reduced patients’ chance of dying by 42%. The trial also found a lower hazard of distant spread or death, another combined measure.

The question of whether patients live longer remains open. Merck and Moderna say their overall survival data are not yet mature and the trial is continuing. Professor Alan Melcher of the Institute of Cancer Research, who was not involved in the study, told the BBC the results were “very impressive” but cautioned that longer follow-up was needed and that success in melanoma could not be assumed for other cancers.

There were costs to treatment as well as potential benefits. The companies reported grade 3–5 treatment-related adverse events in 14.2% of patients treated with the combination and 13.4% of those treated with pembrolizumab and placebo. Fever and injection-site pain were more common with intismeran.

The companies released the detailed results on 22 October ahead of a scheduled cancer conference presentation. They say a paper has been accepted by *The New England Journal of Medicine* and that they are speaking with regulators. Neither step establishes that the treatment has been approved.

Update

Moderna shares fell sharply after details of a melanoma-vaccine trial appeared ahead of a planned presentation, with the company’s stock dropping a further 7.1% in Friday trading, according to Dutch news agency ANP. Merck, Moderna’s partner in developing the treatment, fell 1.9%.