Melanoma vaccine cuts recurrence and death risk 42%

A recent Phase III trial of the personalized mRNA vaccine intismeran, made by Moderna and Merck, shows a 42 percent reduction in melanoma recurrence or death when added to the immunotherapy drug Keytruda. The study enrolled 1,137 patients who had high‑risk melanoma surgically removed and were at stages IIB through IV. Researchers presented the findings at the European Society for Medical Oncology meeting in Madrid. Intismeran is tailored to each patient’s tumor by sequencing the cancer’s unique neoantigens, a fingerprint of abnormal proteins the immune system can target. These results suggest personalized vaccines may improve outcomes beyond standard checkpoint inhibitors.

How the vaccine works

The vaccine trains the immune system to recognize and destroy cancer cells showing those neoantigens, acting like a personalized wanted poster for the tumor. Patients reported only mild, transient side effects such as injection‑site pain, a low‑grade fever, headache or chills—similar to COVID shots. Because the vaccine is made from the patient’s own tumor tissue, it must be produced individually, but the process can finish in roughly nine weeks.

In the trial, 757 patients received intismeran plus Keytruda while 380 received a placebo and Keytruda. After two years, 82 percent of those who received the vaccine were recurrence‑free compared with 70 percent in the placebo group. The analysis gave a hazard ratio of 0.58 with a 95 % confidence interval of 0.45–0.75 and a p‑value less than 0.001, confirming a 42 percent risk reduction. The study spanned 157 sites worldwide, including many Australian centers.

Investors reacted negatively when the findings leaked, and Moderna’s stock fell. Dr. Shirin Bajaj suggested this may be because the difference between the vaccine plus Keytruda and Keytruda alone is still relatively modest. Scaling the personalized vaccine will require overcoming logistical challenges, such as obtaining enough tumor tissue from every patient. The trial’s success opens testing the vaccine in metastatic melanoma and other cancers, and regulatory review will be the next step before it can become available. If approved, the approach could redefine how clinicians use immunotherapy to keep melanoma patients disease‑free longer.