A personalised cancer vaccine given alongside the immunotherapy drug Keytruda reduced the risk of melanoma patients dying or their cancer returning by 42% in a trial of 1,137 adults, according to results presented at the European Society of Medical Oncology conference. The combination also cut the risk of melanoma spreading by 38% over two years compared to immunotherapy alone.
The vaccine, called Intismeran, uses mRNA technology to train each patient's immune system to recognise their own cancer cells. Researchers extracted genetic information from individual tumours to personalise each dose. About two-thirds of trial participants received the vaccine alongside Keytruda, while the rest got a placebo and the immunotherapy drug.
The trial enrolled patients who had already had their tumour surgically removed. MSD (Merck in the US) and Moderna developed the approach and now say they are testing it against kidney, bladder and lung cancers as well.
Trial participant Tony Chapman, 75, was diagnosed with melanoma in 2019 and had a recurrence under his arm. He enrolled in the study but remains unaware whether he received the vaccine or placebo. Three years after starting treatment, he is cancer-free and undergoes six-monthly check-ups.
Independent cancer experts called the results impressive but cautioned that longer-term data remain essential. Prof Alan Melcher from the Institute of Cancer Research in London said the trial represents "an important proof of principle" but warned against assuming the approach will work equally across all cancer types. He noted that overall survival benefit has not yet been demonstrated and longer follow-up is needed.
The results have not yet appeared in a peer-reviewed journal. Both companies said they expect to engage with regulators about approval as soon as next year, though widespread NHS adoption will depend on cost. Each patient requires tumour analysis and a bespoke vaccine manufactured individually.
Stock markets initially surged on news of the trial success, but investors sold shares on Thursday after analysts said the results fell short of earlier, smaller trials. The full trial will continue to monitor participants for cancer recurrence and long-term survival outcomes.