Personalized mRNA Melanoma Vaccine Cuts Recurrence Risk 42% in Phase 3, but Survival Data Are Not In

Adding a personalized mRNA vaccine to the immunotherapy drug pembrolizumab cut the risk of melanoma coming back or causing death by 42 percent in a phase 3 trial of 1,137 patients. That is the figure from the first full dataset on intismeran autogene, made by Merck and Moderna, and it is real. It is also smaller than the 49 percent drop that an earlier, much smaller trial suggested, and the trial has not yet shown that patients live longer.

What the trial measured

The trial, called INTerpath-001, enrolled patients whose melanoma had been completely removed by surgery but who faced a high risk of relapse: stages IIB through IV. Two of every three were assigned to the vaccine plus pembrolizumab (sold as Keytruda). The rest got pembrolizumab with a placebo. The vaccine is built from each patient's own tumor and encodes up to 34 patient-specific mutations, according to AJMC. Treatment ran for about a year.

At two years, 82.2 percent of patients on the combination had no recurrence, against 70.0 percent on pembrolizumab alone. For distant spread, the figures were 88.5 percent and 80.2 percent. Median recurrence-free time was not reached in either group, which means more than half of patients in both arms were still recurrence-free when the data were cut.

The data first reached the public by accident. BioSpace reported that results were posted online on Thursday, October 22, days ahead of a scheduled presentation at the ESMO Congress in Spain, and then removed. Merck released the figures that afternoon. AJMC reports the data have been accepted by the New England Journal of Medicine. This article has not seen the full paper, so it runs on the company release and trade reporting.

The six-month gap

The curves did not separate right away. In the first six months, the hazard ratio for recurrence or death was 0.99, essentially no difference (95% confidence interval 0.66 to 1.49). After six months it fell to 0.42, according to AJMC. The reason for the delay is not established in the reporting. The vaccine is given in up to nine doses three weeks apart. The six-month split was a prespecified sensitivity analysis, not the primary comparison, and it should be read as supporting detail rather than the headline.

Georgina Long, the trial's principal investigator and medical director of Melanoma Institute Australia, said in the companies' statement that the work has the potential to establish a new treatment paradigm after surgery for melanoma. That is her assessment and the sponsors' wording, and survival data have not yet backed it up.

Safety, and what investors read into it

Treatment-related adverse events occurred in 95.8 percent of patients on the combination and 90.0 percent on pembrolizumab alone. Serious events, grade 3 to 5, were close: 14.2 percent versus 13.4 percent. The most common reactions to the combination were fever in 52.2 percent, injection site pain in 51.0 percent, and fatigue in 38.5 percent. No new safety signals were reported, per AJMC.

Markets read the result differently from clinicians. Moderna shares fell 21 percent after the leak, BioSpace reported, because the hazard ratio landed at the low end of what analysts had hoped for. RBC Capital Markets said regulatory approval looked likely but that commercial success was far less certain. It pointed to a comparison the trial did not make: pembrolizumab given before surgery, which RBC says may offer similar benefit at lower cost. BMO Capital Markets cautioned against assuming the result carries over to other tumor types. Jane Healy of Merck answered that the benefit is not subtle.

Where the earlier number came from

The 49 percent figure cited in earlier coverage comes from a separate phase 2b trial. Merck's release reports a hazard ratio of 0.51 there, with a wide confidence interval of 0.294 to 0.887. The phase 3 estimate sits inside that range, and its interval, 0.45 to 0.75, is much tighter.

The effect needs about six months to show, the safety profile looks close to pembrolizumab alone in serious events, and no one has reported a survival difference. Patients with resected melanoma and their oncologists are the people who decide what to do with this, and none of it is medical advice. The full ESMO presentation and the journal paper are the documents that will settle the open questions, including how many events drove each analysis.