When news came in August 2026 that what may be the first messenger RNA (mRNA)-based cancer vaccine had succeeded in an advanced clinical trial for treating melanoma, there was jubilation among oncologists and the public alike. This was before the vaccine developers revealed the effectiveness of this treatment.
Now, the effectiveness of the vaccine has been revealed.
Patients who received the experimental vaccine, along with the approved drug Keytruda, were shown to have a 42% lower risk of their cancer coming back after surgery or death than those who received Keytruda alone, opening the door to an entirely new approach to treating this disease.
“This new vaccine represents something we haven't seen before, both in terms of the level of efficacy that it has shown and in terms of how it works,” Dr. Michael Busto, chief of melanoma at Memorial Sloan Kettering Cancer Center, told CNN.
The vaccine is currently known as "intismeran autogene" until it receives a trade name.
Merck and Moderna, developers of the experimental vaccine, released the data early Thursday, following reports it was posted online and later removed.
The companies said in a press release that they are "working with regulatory agencies" based on these findings, indicating they may apply for FDA approval soon.
The two companies are also currently working on testing this technology to combat other types of cancer, including lung cancer and pancreatic cancer.
This experimental vaccine uses the same messenger RNA (mRNA) technology that was used in the Moderna COVID-19 vaccine. But instead of training the immune system to fight an invading virus, the vaccine works to boost the immune system's ability to fight cancer cells more aggressively.
The vaccine is also designed specifically for each patient, based on the genetic fingerprint of his or her tumor.
After the tumor is surgically removed, a sample is taken and genetically analyzed, and the vaccine is then designed based on the indicators in the tumor that are most likely to stimulate a strong immune response.
“This cancer vaccine is a unique type of treatment, as it enhances the body’s immune response only to the patient’s existing cancer cells,” Busto explained.
Busto worked with patients in the trial, including Beth Rezick, 59, who was diagnosed with stage III C melanoma in December 2023.
This stage means that the tumor has reached a certain thickness in the skin and has spread to the lymph nodes, making it more likely that it will return after surgery.
“We wish that surgery alone was enough to achieve a cure,” Busto said, “but we know from numerous studies that patients in this situation face a high probability of the cancer coming back in other locations, whether in additional lymph nodes or other parts of the body, such as the bones, liver, lungs, or brain.”
Patients are then prescribed a treatment aimed at preventing this from happening, known as “adjuvant therapy”, that is, treatment given after the primary treatment, which in this case is surgery.
This treatment is usually a drug like Keytruda, which caused a revolution when it was approved in 2014. This drug works by enabling the immune system to attack cancer cells that may have remained hidden.
The drug "Keytruda" was famously used to treat former US President Jimmy Carter from skin cancer that had spread to his liver and brain. Carter announced that he was cancer-free in December 2015.
Until now, Rezek (like the rest of the 1,136 trial participants) does not know whether she received the experimental vaccine or a placebo along with Keytruda (which all participants received).
However, she believes she actually received the vaccine, because she felt “a little unwell, flu-like, with a general feeling of fatigue the next day” after each treatment session.
The experimental vaccine, or placebo, was given by intramuscular injection every three weeks, for a maximum of nine doses, while Keytruda was given by intravenous injection every six weeks for up to about a year.
So Resik wasn't always receiving both treatments at the same time.
But she is certain that she is still cancer-free more than a year after completing her treatment within the trial.
The trial results showed a 42% reduction in the risk of cancer recurrence based on data collected an average of about two years after starting treatment. The trial will continue to evaluate other indicators.
Rezick hopes that others will have the opportunity to benefit from this new approach to cancer treatment, and that its price will not be so high that patients cannot afford it.
Pharmaceutical companies usually do not announce the price of a drug until it has been officially approved.
