A personalized cancer vaccine cut the risk of melanoma coming back or the patient dying by 42 percent in a phase 3 trial, researchers reported at the ESMO Congress in a presentation that reframes what a vaccine can be used for.
The vaccine, intismeran, is made from each patient's own tumour. It was given alongside pembrolizumab, a standard immunotherapy, to 1,137 people whose melanoma had been surgically removed but who were at very high risk of recurrence: stage IIB to IV, with no earlier drug treatment.
How the vaccine works
Traditional vaccines are given to healthy people to prevent disease. Intismeran is therapeutic. It is designed for people who already have had cancer, and it teaches the immune system to recognise the specific mutations in that patient's tumour so leftover cancer cells are less likely to grow into advanced disease.
The trial compared intismeran plus pembrolizumab against pembrolizumab alone. Adding the vaccine reduced the risk of recurrence or death by 42 percent, with a hazard ratio of 0.58 and a confidence interval of 0.45 to 0.75. For patients who remained recurrence-free beyond six months after starting treatment, the reduction reached 58 percent.
Side effects stayed manageable
The vaccine did not add to the side effects of pembrolizumab. Most reactions were transient and low grade: injection-site pain, headache and chills in some patients.
"These results showed that patients with earlier-stage melanoma can be treated after surgery in a fundamentally new way," said Professor Georgina Long, medical director of Melanoma Institute Australia and chair of melanoma medical oncology at the University of Sydney.
Why this one is different
Personalized cancer vaccines have been promised for years and have mostly failed to clear large trials. What changed is the speed of sequencing a tumour and manufacturing a matched vaccine, plus a clearer understanding of which mutations the immune system can actually see.
The next questions are practical: cost per patient, manufacturing time, and whether the approach holds up in tumours with fewer mutations than melanoma, which is one of the most mutation-heavy cancers. For now, the result gives oncologists a new option to test after surgery, in the window where recurrence is most likely.