What to Know About the New Cancer Vaccine

4 min read

Conversations about cancer research are tough for anyone who has ever been diagnosed, treated, or lost someone to the disease. But ongoing tests of a Moderna vaccine are giving new hope and sparking much discussion about fighting and curing cancer. Pharmaceutical companies Moderna and Merck first announced plans to collaborate on personalized mRNA cancer vaccines back in 2016. As of August 2026, the latest round of testing, now in its third phase, shows positive results for specific types of cancer patients. Here’s everything you need to know about the cancer vaccine, according to a medical professional.

The words cancer and vaccine seem about as paradoxical as the age-old chicken-or-egg debate; however, Lucy M. De La Cruz, MD, FACS, who is the chief of the Breast Surgery Program and associate professor of surgery at MedStar Georgetown University Hospital, explains to ELLE that Moderna’s cancer vaccine (called intismeran autogene, or mRNA-4157) isn’t like the shots we know that prevent COVID or HPV. “It’s a treatment for people who already have cancer, and it’s still experimental, meaning it isn’t yet FDA-approved,” she says. According to De La Cruz, doctors give the treatment alongside an existing immunotherapy drug called Keytruda (pembrolizumab).

What types of cancers does mRNA-4157 treat?

So far, the strongest results are in melanoma, which De La Cruz notes is the most dangerous type of skin cancer. “In a study of patients whose high-risk melanoma had been surgically removed, adding the vaccine to Keytruda cut the risk of the cancer returning or spreading (or of death) by roughly half, compared with Keytruda alone. Five years later, the benefit was holding,” she notes.

Larger studies are now underway in other cancers, including lung, kidney, bladder, and another type of skin cancer. Other companies are also testing personalized vaccines for pancreatic and triple-negative breast cancer. “This is a fast-moving field, but for Moderna’s vaccine, melanoma is the only cancer with proven results so far,” says De La Cruz.

Does the vaccine give you cancer?

This treatment seemingly goes against everything we know vaccines to be, including what they do in the body to treat or prevent its intended illness. At the most basic level, vaccines pump small doses of the illness they’re trying to prevent into the body to trigger the immune system to create antibodies that block these invaders if ever presented in higher viral loads. With mRNA-4157, De La Cruz explicitly says that “No, this shot does not contain any cancer cells whatsoever and cannot give anyone cancer.”

How does the cancer vaccine work in the body?

She says to think of this shot as a wanted poster for your immune system. “Every tumor carries small genetic errors that make its cells look slightly different from healthy ones.” Each dose is personalized specifically to the patient and starts with a doctor analyzing a sample of the patient’s tumor and a blood sample to identify the unique markers on that person’s cancer. A computer selects the markers most likely to catch the immune system’s attention, and instructions for up to 34 of those markers are packaged into mRNA, a temporary genetic message, and wrapped in a tiny fat bubble (the same delivery method used in the COVID vaccines).

Once the shot is administered, the patient’s cells read the message and briefly display those markers, teaching the immune cells to recognize and destroy any cancer cells carrying them. “The mRNA breaks down quickly and does not change your DNA,” De La Cruz points out. Keytruda plays a supporting role by, as De La Cruz puts it, “Taking the ‘brakes’ off your immune cells so they can do their job more forcefully.” Every dose is custom-made from the patient’s own tumor, making this a complex, time-intensive process, and not an off-the-shelf shot like other vaccines.

The shot requires multiple doses. De La Cruz explains that in the melanoma study, patients received up to nine doses of the vaccine, one every three weeks, along with up to 18 Keytruda infusions over about a year.

Are there side effects to mRNA-4157?

According to De La Cruz, side effects have been manageable overall among patients in the trials—and no new safety concerns have surfaced even five years after the tests began. She adds that most side effects reported were mild to moderate and similar to what people experience with other vaccines:
∙ Soreness or redness where the shot was given (about 7 in 10 patients)
∙ Fatigue (about 6 in 10)
∙ Chills (about half)
“Adding the vaccine did not increase serious immune-related side effects compared with Keytruda alone, and no life-threatening or fatal side effects were linked to the vaccine itself,” says De La Cruz, also noting that serious reactions can still happen and have historically been mostly tied to Keytruda, which she clarifies is already a standard, well-understood drug. “About 12 percent of patients stopped treatment because of side effects.”

Who are the best candidates for the cancer vaccine?

Of course, who qualifies for the vaccine is best determined by a patient’s individual doctor, but De La Cruz says the proven benefit is for people whose cancer has been removed and who are essentially cancer-free after surgery. “The vaccine’s job is to hunt down tiny leftover cancer cells and keep the disease from coming back,” she adds. “It is not designed to shrink large, established tumors. In earlier studies of patients with advanced, active melanoma, the vaccine plus Keytruda helped only a small share of patients, so its usefulness in that situation is far less certain. Researchers are still studying it,” she concludes.