Intismeran cuts melanoma recurrence by 42%: what the phase III data really shows

On 23 October 2026, researchers announced results from an international phase III trial of intismeran, a personalised mRNA cancer vaccine made to target genetic mutations unique to each patient's melanoma. It is the first individualised cancer vaccine to post positive results at this stage of testing.

The trial enrolled 1,137 patients whose melanoma had been surgically removed but who were at high risk of recurrence. All received the immunotherapy pembrolizumab (Keytruda) for twelve months. Some also received intismeran, custom-built from their own tumour's genetics.

At two years, the combination cut the risk of recurrence or death by 42% compared with pembrolizumab alone. It cut the risk of cancer spreading or death by 38%. About 82% of patients on the combination were still alive.

Professor Georgina Long, Medical Director at Melanoma Institute Australia and Chair of Melanoma Medical Oncology and Translational Research, presented the findings.

Phase III is the test that matters. Earlier-stage trials establish safety and hint at benefit; phase III compares the new treatment against the current standard in a large population, and its results are what regulators weigh. A 42% relative risk reduction at two years is a substantial effect size in a cancer with high recurrence rates after surgery.

Several caveats belong alongside that number. The data cover two years; whether the benefit persists at five or ten years is unknown. And the vaccine is not approved or available — these are trial results, not a licensed product. No regulatory timeline has been confirmed.

What the result does establish is proof of concept at scale. Personalised mRNA vaccines have been theorised for years; this is the first to clear the phase III bar in any cancer. The same platform is now being tested in kidney, bladder and lung cancers, where the mutation-targeting logic may or may not transfer.

For readers in high-melanoma countries, the context is direct. Australia has one of the world's highest melanoma rates, with one person diagnosed every 30 minutes. If the two-year data hold and regulators accept them, post-surgery melanoma care could shift from a generic protocol to a bespoke vaccine built from each patient's tumour.

That is a real shift in how oncology works. It is not yet a cure, and it is not yet available. It is the strongest evidence so far that the approach can work.