Intismeran vaccine reduces melanoma recurrence by 42% in major trial

A personalised cancer vaccine given alongside the immunotherapy drug Keytruda cut the risk of death or melanoma returning by 42 % in a large clinical trial, researchers reported on Thursday. The study involved 1,137 adults who had surgery to remove their tumours, and it showed a 38 % reduction in the chance of the cancer spreading over two years compared with immunotherapy alone.

The trial tested a new mRNA‑based vaccine called Intismeran, which is customised for each patient using genetic information from their own tumour. The approach builds on the success of Covid‑19 mRNA shots, but instead of targeting a virus it trains the immune system to recognise cancer cells. Participants received the standard Keytruda treatment, and about two‑thirds also received the experimental vaccine while the rest got a placebo. The study focused on patients whose tumours had already been removed, aiming to stop any hidden cancer cells from growing back.

Results showed that patients who received the vaccine were far less likely to see melanoma recur or spread. Over the two‑year follow‑up, the vaccine group had a 42 % lower risk of death or disease return and a 38 % lower risk of metastasis. Experts called the findings impressive but cautioned that longer‑term data are needed. “Personalisation is the next step up and it’s really exciting,” said Prof Pippa Corrie, an oncologist at Addenbrooke’s Hospital who helped run the study. She added that the trial was the first proof of principle for this technology. Patients like 75‑year‑old Tony Chapman, who volunteered for the trial after a second tumour appeared, remain cancer‑free three years later, though he still does not know whether he received the vaccine or a placebo.

The manufacturers MSD (Merck in the US) and Moderna say they are already testing the same approach in kidney, bladder and lung cancers. Shares in both companies rose after the initial hint of success in the summer, but fell on Thursday after analysts said the results were not as dramatic as earlier, smaller studies suggested. If longer‑term studies confirm the benefit, the vaccine could become a new standard for preventing melanoma recurrence and may open the door to personalised vaccines for many other tumour types.