Merck and Moderna said a made-to-order cancer treatment helped keep high-risk melanoma from returning or spreading after surgery in a large late-stage trial, moving personalized mRNA vaccines closer to routine cancer care.
The companies and Reuters described the interim result as the first positive Phase 3 finding for both an mRNA-based cancer therapy and a treatment individually designed around the mutations in each patient’s tumor. Phase 3 trials are generally the last major testing stage before a company seeks approval.
Despite the shorthand “cancer vaccine,” intismeran is not intended to prevent melanoma in healthy people. It is a treatment for people whose cancer has already been removed but who remain at substantial risk that unseen cancer cells will seed another tumor.
To make it, a sample of the removed tumor is analyzed for mutations. Moderna then produces a unique strand of messenger RNA encoding as many as 34 tumor-specific targets. After injection, the mRNA prompts cells to display those targets, teaching the immune system what that patient’s cancer looks like.
Intismeran was paired with Keytruda, Merck’s widely used immunotherapy, which releases a brake that cancer can place on immune cells. The aim is to show the immune system its targets while helping it attack them.
The randomized, double-blind trial enrolled 1,137 people with stage IIB through IV skin melanoma that had been completely removed. Participants received either Keytruda alone or Keytruda plus as many as nine doses of intismeran during roughly a year of treatment.
At a planned interim analysis, the combination met the study’s main goal: patients went longer without their cancer returning or dying. It also met a key secondary goal measuring how long patients survived without the cancer spreading to a distant part of the body. Merck and Moderna characterized both improvements over Keytruda alone as statistically significant and clinically meaningful.
The announcement contained no hazard ratios, absolute recurrence rates or survival curves. That means outside researchers cannot yet judge how large the benefit was, how many patients avoided a recurrence or how the results changed over time.
It is also unknown whether intismeran helps patients live longer. The trial is continuing to track overall survival, and the companies said detailed findings would be presented at a medical meeting. They reported no new safety signals, but the announcement did not provide detailed side-effect rates.
Intismeran remains experimental. Merck and Moderna plan to discuss regulatory submissions, but they have not announced an approval or even a filing. Still, succeeding in a 1,137-person trial against an established treatment is pivotal evidence that a therapy manufactured separately for every patient can work beyond a small experimental study.
The companies are testing the approach in other cancers, including lung, bladder and kidney tumors. The melanoma result does not establish that it will work in those diseases, but it gives the broader idea of made-to-order cancer medicine its strongest clinical validation yet.