A new clinical trial shows that personalized messenger RNA vaccines against high-risk skin cancers reduce the risk of recurrence and death by almost 50% over five years, compared to standard treatment alone. This is an announcement from Moderna and Merck, the two pharmaceutical manufacturers collaborating on this project, relayed by the online media Ars Technica.
The press release, published on January 20, 2026, currently only reports the main results. These, however, are consistent with more detailed analyzes from earlier testing phases, which looked at recurrence and death rates at earlier time points, two and three years after treatment. More data on this new experimental phase – the second – will appear soon. The third phase, the last step before marketing, has also been launched.
Phase 2 in question included 157 patients suffering from melanoma, a skin cancer, stage 3 or 4, for whom the risk of recurrence after their surgical removal is high. For them, the standard treatment is immunotherapy, with Keytruda from the Merck brand. This medicine activates immune cells, especially T lymphocytes, to destroy cancer cells. T cells are already supposed to do this, but in some cases, cancer cells can bind to their receptors and thus neutralize them. Keytruda therefore ensures that it blocks access to these receptors and allows the T lymphocytes to do their job.
Mild side effects
The experiment thus compares the effectiveness of the vaccine in addition to Keytruda to a similar treatment but without vaccine. All 157 patients took Keytruda and two thirds also received a messenger RNA vaccine. Each vaccine was personalized to suit each patient’s melanoma specifically, carrying the genetic instructions to produce up to 34 markers of their cancer cells. Inside the body, healthy cells reproduce these markers and use them to train T lymphocytes to identify and attack cancer cells: this is the principle of the vaccine.
After two years, 24 of the 107 patients who received the experimental vaccine in addition to treatment died or suffered a recurrence, or 22%. This is almost double for the group which was content with simple treatment, in which there were 20 deaths or recurrences out of 50 patients, that is to say 40%. This therefore gives a risk reduction of 44% for the cancer vaccine. This figure increased to 49% after three years. Same thing after five years, as indicated in this week’s press release, without giving details among the two groups.
The side effects otherwise remain low and controlled. Moderna and Merck note the same observations as in previous phases, namely that the most common side effects linked to vaccines are fatigue, pain at the site of the injection as well as chills.
These results “illustrate the potential for prolonged benefit” for this vaccine against skin cancer “when combined with Keytruda”enthuses Kyle Holen, vice-president of Moderna. They “also show the potential of messenger RNA to fight cancer”he adds, specifying that his company is currently carrying out eight other clinical trials in phases 2 or 3 for vaccines against other cancers, notably lung, bladder and even kidney.
While the main results appear promising, no conclusions can be drawn until the full publication of the trial data, notes Ars Technica. But the biggest obstacle on the road to messenger RNA cancer vaccines will be far more political than technical. The famous American Secretary of Health Robert F. Kennedy Jr. is a fervent anti-vaxxer who multiplies lies about their safety and effectiveness. In August 2025, “RFK Jr.” unilaterally canceled a grant of 500 million dollars (approximately 421 million euros) intended for the development of messenger RNA vaccines.
