Breakthrough New Vaccine Slashes Chances of Deadly Skin Cancer Returning After Treatment

An experimental vaccine designed from a sample of each patient’s own tumour lowered the risk of the skin cancer melanoma coming back or causing death by 42% in a large international trial, the drug companies MSD, known as Merck in the United States and Canada, and Moderna reported on 22 October 2026.

MSD makes the cancer drug Keytruda and Moderna is known for its Covid-19 vaccine, and the two developed the vaccine together.

The trial involved 1,137 patients whose melanoma, from stage 2B to stage 4, had been completely removed by surgery, and they were randomly placed in one of two groups, one given the vaccine with Keytruda, an immunotherapy drug already used after surgery, and the other given Keytruda with a placebo, a dummy treatment with no medicine in it.

Memorial Sloan Kettering Cancer Center in New York explains that melanoma is staged from 0 to 4, and the higher the number, the further the cancer has spread.

Stage 2B is a thicker tumour that has not reached the lymph nodes, small structures that help the body fight infection, while stage 3 most often means it has reached nearby lymph nodes and stage 4 means it has spread further, to areas such as the liver, lungs or brain.

At two years, 82% of patients given the vaccine were alive and without the cancer coming back, against 70% of those given Keytruda alone, according to the companies, which works out to about 12 more people in every 100.

Side effects linked to the treatment were common in both groups, affecting about 96 in every 100 patients given the vaccine with Keytruda and 90 in every 100 given Keytruda alone, with fever, pain where the injection was given and tiredness the most common in the vaccine group, while severe side effects affected around 13 to 14 in every 100 patients in each group.

It is not yet known whether the vaccine helps patients live longer, because that part of the trial is still running, and it remains experimental, with the companies saying they are engaging with regulators, the bodies that decide whether a medicine can be used.

Souurces:Merck and Moderna, 22 October 2026; Long G, et al. INTerpath-001, ESMO Congress 2026, 24 October 2026; University of Sydney, 23 October 2026; Memorial Sloan Kettering Cancer Center, Melanoma Stages, 31 October 2026