TL;DR: Moderna and Merck's personalized mRNA therapy intismeran autogene plus pembrolizumab cut recurrence or death by 42% in resected stage IIB-IV melanoma in the phase 3 INTerpath-001 trial.

Trial Hits Primary Goal In Resected Melanoma

Moderna and Merck reported that the combination of intismeran autogene with pembrolizumab lowered recurrence or death risk by 42% versus pembrolizumab alone among people with completely resected stage IIB-IV melanoma, according to Ars Technica.

The finding came from detailed results of the phase 3 INTerpath-001 study, identified as NCT05933577, after complete surgical removal of melanoma tumors, according to the American Journal of Managed Care (AJMC).

The companies disclosed the outcomes on Oct. 22, 2026, after a leak online that morning prompted release of key data ahead of a planned scientific presentation, according to Nature.

Full data were scheduled for Presidential Symposium I at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid on Oct. 24, and had been accepted for publication in The New England Journal of Medicine, according to AJMC.

The disclosure followed an August announcement by Merck and Moderna that the trial had met its primary endpoint of recurrence-free survival (RFS) and its key secondary endpoint of distant metastasis-free survival (DMFS), according to AJMC.

Merck, based in Rahway, New Jersey, and Moderna, headquartered in Cambridge, Massachusetts, developed the regimen together, according to Nature.

How The 42% Reduction Was Measured

After a median follow-up of 24.6 months, the hazard ratio for recurrence or death was 0.58, with a 95% confidence interval of 0.45-0.75 and P < .001, according to AJMC.

The hazard ratio for distant metastasis or death was 0.62, equal to a 38% lower risk, with a 95% confidence interval of 0.45-0.85 and P = .002, according to AJMC.

The two-year RFS rate was 82.2% for intismeran plus pembrolizumab compared with 70.0% for pembrolizumab alone, according to AJMC.

The two-year DMFS rates were 88.5% and 80.2%, respectively, according to AJMC.

Median RFS and DMFS had not been reached in either treatment arm at the analysis point, according to AJMC.

Investigators described improvements as generally consistent across prespecified subgroups, according to AJMC.

Participants will continue to be monitored for several years to determine whether vaccination improves overall survival, according to Nature.

Overall survival data were not yet mature at release, although the companies reported a favorable trend, according to AJMC.

Who Enrolled And What They Received

The trial randomly assigned 1,137 patients in a 2:1 ratio after complete surgical resection, according to AJMC.

Participants had moderate to advanced melanoma and enrolled across 157 centers, according to Nature.

One group received intismeran 1 mg every three weeks for up to nine doses plus pembrolizumab 400 mg every six weeks for up to nine cycles, according to AJMC.

The comparison group received placebo plus pembrolizumab on the same pembrolizumab schedule, according to AJMC.

Treatment duration was approximately one year, according to AJMC.

Pembrolizumab, sold as Keytruda by Merck, is already used to treat melanoma, according to Nature.

The vaccine, called intismeran, is not designed to prevent melanoma from developing initially, but to stop it returning in people who already underwent surgery to remove tumors, according to Nature.

Personalized mRNA Built For Each Tumor

Intismeran autogene, also identified as V940 or mRNA-4157, is an investigational individualized neoantigen therapy, according to AJMC.

Each dose is produced from the individual patient's tumor sample, according to AJMC.

The product consists of synthetic mRNA coding for up to 34 neoantigens unique to that patient's cancer, according to AJMC.

To create it, researchers sequenced DNA from a sample of each participant's tumor to identify mutations in cancer cells, according to Nature.

Those mutations can give rise to proteins called neoantigens, which help distinguish cancer cells from healthy ones, according to Nature.

Moderna CEO Stéphane Bancel said in a statement:

"From the beginning, we believed mRNA technology could make it possible to develop cancer treatments uniquely matched to each patient's tumor."

Bancel described the results as a defining moment for that vision and said they reinforce the company's conviction that mRNA has potential to fundamentally change cancer treatment, according to Ars Technica.

Study principal investigator Professor Georgina Long, medical director of Melanoma Institute Australia and Chair of Melanoma Medical Oncology and Translational Research at the University of Sydney, said the findings support an individualized approach that tailors treatment to a tumor's mutational signature to enhance anti-tumor immune response, according to AJMC.

Benefit Appeared After Vaccination Series

During the first six months, efficacy was comparable between arms, according to AJMC.

The hazard ratio for recurrence or death during that early period was 0.99, with a 95% confidence interval of 0.66-1.49, according to AJMC.

The hazard ratio for distant metastasis or death during the same period was 1.01, with a 95% confidence interval of 0.58-1.79, according to AJMC.

After six months, following completion of the intismeran regimen, a prespecified sensitivity analysis showed stronger separation, according to AJMC.

In that later period, risk of recurrence or death was reduced by 58%, for a hazard ratio of 0.42 with a 95% confidence interval of 0.30-0.58, according to AJMC.

Risk of distant metastasis or death after six months was reduced by 50%, for a hazard ratio of 0.50 with a 95% confidence interval of 0.34-0.73, according to AJMC.

In a modified intention-to-treat analysis that excluded participants who did not receive at least one dose of intismeran or placebo as planned, reductions were 49% for recurrence or death and 45% for distant metastasis or death, according to AJMC.

The corresponding hazard ratios in that analysis were 0.51, with a 95% confidence interval of 0.39-0.67, and 0.55, with a 95% confidence interval of 0.40-0.77, respectively, according to AJMC.

Safety Profile Largely Mirrors Pembrolizumab Alone

Treatment-related adverse events occurred in 95.8% of patients receiving the combination and 90.0% receiving pembrolizumab alone, according to AJMC.

Grade 3-5 treatment-related adverse events occurred in 14.2% and 13.4%, respectively, according to AJMC.

The most common adverse events with the combination were pyrexia at 52.2%, injection-site pain at 51.0%, and fatigue at 38.5%, according to AJMC.

No new safety signals were observed, according to AJMC.

Trial leader Georgina Long said the therapy did not result in any major harmful side effects, according to Nature.

The companies said they are engaging with regulatory authorities to seek approval, according to Ars Technica.

If authorized, the regimen could become the first approved mRNA vaccine for cancer, according to Nature.

Context For Patients And Next Research

Roughly 15 years ago, people with advanced melanoma typically survived for only months, according to Nature.

Today, nearly 55% are effectively cured with targeted drugs or immunotherapies, according to trial leader Georgina Long as reported by Nature.

Long said the combination is designed for people whose cancer could return after surgery and who do not respond to immunotherapy alone, according to Nature.

Oncologists regard a 10% risk reduction as substantial, said immunotherapist Kristen Radford of Mater Research in Brisbane, according to Nature.

Geneticist Seth Cheetham of the University of Queensland in Brisbane said a reduction above 40% would send many researchers over the Moon, according to Nature.

Cancer geneticist Jessamy Tiffen of the Centenary Institute in Sydney said the results are exciting, but only time will tell how effective treatment is beyond two years, according to Nature.

Tiffen noted cancer cells have an ability to adapt and evade treatment and that some people did not respond to vaccination, according to Nature.

Long said her team will conduct statistical analysis to identify who is most likely to benefit, according to Nature.

Merck and Moderna are evaluating intismeran in nine phase 2 and phase 3 trials across multiple tumor types, including three ongoing phase 3 trials in non-small cell lung cancer, according to AJMC.

Investors had anchored expectations on the earlier phase 2b KEYNOTE-942 study, in which the combination produced a hazard ratio of 0.51 for recurrence or death, according to RBC Capital Markets as reported by AJMC.

Moderna shares fell 21% after release, while another account put the post-leak decline around 25%, reflecting inflated expectations ahead of full data rather than a judgment on combination efficacy, according to AJMC and Nature.

Health-care financial analyst Evan Seigerman at BMO Capital Markets in New York City told Forbes that market reaction probably reflected inflated expectation into full data release rather than a true indictment of combo therapy efficacy, according to Nature.

Sources referenced