An individualised mRNA neoantigen therapy held its melanoma benefit at five years

Design

randomised phase IIb, open-label, 2:1 allocation; five-year descriptive update

Population

157 patients with resected stage IIIB-IV cutaneous melanoma; median follow-up 60.3 months

Primary outcome

recurrence-free survival

Effect

recurrence-free survival HR 0.510 (95% CI 0.294-0.887); distant metastasis-free survival HR 0.411 (0.200-0.843); overall survival HR 0.471 (0.165-1.345)

KEYNOTE-942 randomised 157 patients with resected stage IIIB to IV cutaneous melanoma 2:1 to intismeran autogene - an mRNA-based individualised neoantigen therapy, formerly mRNA-4157 or V940 - given as nine intramuscular doses alongside 18 doses of pembrolizumab, or to pembrolizumab alone for 18 doses. The primary endpoint was recurrence-free survival. This is the five-year descriptive update, at a median follow-up of 60.3 months.

The recurrence-free survival benefit persisted (hazard ratio 0.510, 95% CI 0.294-0.887), as did distant metastasis-free survival (HR 0.411, 95% CI 0.200-0.843). Overall survival favoured the combination but did not separate statistically (HR 0.471, 95% CI 0.165-1.345). Safety remained manageable with no new signals. Correlative work showed greater T-cell receptor clonality and more novel clonotypes with the combination, and greater expansion of novel clones in patients who did not recur.

What makes this a practice-changer is durability rather than novelty: a phase II signal that holds at five years is the kind that survives into phase III, and the confirmatory trial is the thing to watch. What it is not, yet, is available. Individualised neoantigen therapy requires tumour sequencing and bespoke manufacture for each patient, which puts it out of reach of routine Indian practice on cost and logistics regardless of what any regulator decides; there is no CDSCO position on it. The immediate implication is for how adjuvant melanoma is discussed - the standard is still pembrolizumab, and a patient asking about vaccines should be told this is a 157-patient phase II with a confirmatory trial running.

• Adjuvant pembrolizumab remains the standard after resection of high-risk melanoma - nothing here changes that today
• Ensure resected high-risk melanoma is discussed for adjuvant therapy at all, which is where most of the avoidable loss still sits
• Where a patient asks about melanoma vaccines, give them the numbers: 157 patients, phase II, five-year recurrence-free survival benefit, overall survival not yet demonstrated
• Do not describe this as approved or available - it is neither in India
• Keep tissue handling in mind at resection; individualised approaches depend on adequate tumour material

Why it matters

A phase II signal that holds for five years changes how seriously the confirmatory trial should be taken - and what a patient should be told when they ask.

Don't overread it

This is a 157-patient phase IIb trial with descriptive five-year analyses and no demonstrated overall survival benefit.

The statistics, in plain English

A hazard ratio of 0.510 for recurrence-free survival means roughly half the rate of recurrence over the follow-up period, and the interval (0.294-0.887) stays clear of 1.0. Overall survival is the one to read carefully: a hazard ratio of 0.471 looks impressive but its interval runs from 0.165 to 1.345, crossing 1.0 - with only 157 patients there have been too few deaths to tell benefit from chance, so this is an unproven survival effect, not a demonstrated one. Five-year analyses here were descriptive rather than formally powered, which further limits how much weight the numbers carry.

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