Adding Moderna’s in-development cancer vaccine to a standard treatment for melanoma dramatically reduces cancer survivors’ risk of death or recurrence, according to newly shared trial data.

Moderna and pharma giant Merck are developing an mRNA-based cancer vaccine, mRNA-4157 (V940), for people who’ve had high-risk melanomas removed.

The vaccine works by instructing the body to make up to 34 “neoantigens.” These are proteins found only on the cancer cells, and Moderna personalizes the vaccine for each recipient so that it carries instructions for the neoantigens on their cancer cells.

The idea behind the vaccine is that, by prompting the body to make these proteins, it can prepare the immune system to quickly identify and attack any new cancer cells bearing them, preventing recurrence.

What’s new? In the ongoing phase 2b KEYNOTE-942 study, Moderna and Merck are comparing the cancer vaccine’s ability to prevent melanoma recurrence or death when combined with Keytruda, Merck’s FDA-approved cancer treatment, to Keytruda alone.