A PERSONALISED mRNA-based cancer vaccine developed by Moderna and Merck & Co. has delivered a landmark result in a late-stage melanoma trial, strengthening hopes that technology originally propelled into the mainstream by Covid-19 vaccines could eventually become a powerful weapon against cancer.
The companies said the vaccine reduced the rate of melanoma recurrence in a final-stage clinical trial, marking the first time an mRNA-based cancer vaccine has demonstrated success in a large-scale study.
Bloomberg reported on Monday that although Moderna and Merck have yet to disclose the full results or the magnitude of the benefit, the announcement has been welcomed by investors and cancer researchers as a potentially significant turning point for a field that has struggled for decades to translate promising laboratory findings into successful human trials.
The findings could also reinvigorate interest in mRNA technology, which faced widespread scepticism during the Covid-19 pandemic and continues to attract criticism, including from US Health Secretary Robert F. Kennedy Jr.
Investors responded strongly to the announcement, with Moderna shares surging 177% on the day the results were reported.
Unlike conventional vaccines designed to prevent infectious diseases, personalised cancer vaccines are intended to treat people who already have cancer, particularly by reducing the risk of the disease returning after surgery.
The Moderna-Merck approach uses mRNA to instruct cells to produce fragments of mutated proteins, known as neoantigens, found in a patient’s tumour.
The immune system is then trained to recognise those mutations and mount an attack against cancer cells carrying them.
The technology is personalised because cancer mutations vary significantly from one patient to another, even among people diagnosed with the same type of cancer.
Scientists analyse a patient’s tumour sample and use an algorithm to identify mutations most likely to trigger an immune response. The resulting vaccine can contain up to 34 mutations selected specifically for that patient.
Jane Healy, head of oncology early development at Merck, said the number of mutations included in the vaccine provided multiple targets against the patient’s cancer.
“Thirty-four is quite a lot of chances, of shots on goal,” she said, adding that the approach was designed to cover “a sufficient amount of the spectrum of a patient’s cancer”.
The strategy differs from existing cancer treatments such as chemotherapy, targeted drugs and conventional immunotherapy.
Chemotherapy attacks rapidly dividing cells, while targeted medicines block specific proteins that drive cancer growth. Immunotherapy drugs such as Merck’s Keytruda work by disabling mechanisms that allow cancer cells to evade the immune system.
Personalised cancer vaccines instead aim to teach the immune system to identify the specific mutations carried by an individual patient’s tumour.
The approach is particularly suited to patients who have undergone surgery and are at high risk of recurrence, when the remaining cancer burden may be relatively small and more vulnerable to an immune response.
However, important questions surrounding the latest melanoma results remain unanswered.
The companies have not yet released detailed findings, including the size of the reduction in recurrence. Researchers also do not yet know whether patients receiving the vaccine will live longer.
The trial is continuing to collect longer-term data, with the full findings expected to be presented at an upcoming scientific meeting.
The success has nevertheless encouraged wider efforts to develop mRNA-based cancer treatments.
Moderna and Merck are testing their personalised approach in other cancers, including lung, bladder and kidney tumours.
Germany’s BioNTech and Switzerland’s Roche are also developing personalised mRNA cancer vaccines targeting diseases including pancreatic and colon cancer.
BioNTech is separately pursuing a standardised mRNA vaccine approach for patients with advanced lung cancer and head and neck cancer.
Beyond cancer, researchers are also exploring mRNA technology for rare and metabolic diseases, with Moderna testing treatments for propionic acidemia and methylmalonic acidemia.
The latest melanoma findings do not establish mRNA vaccines as a cure for cancer, but they provide some of the strongest clinical evidence yet that the technology can be adapted to train the immune system against an individual patient’s tumour.
For cancer researchers, the results could represent an important step towards making personalised vaccines a practical part of cancer treatment rather than a long-standing scientific ambition. - August 24, 2026
