Could mRNA Vaccines One Day Treat Breast Cancer?

A potential breast cancer treatment relies on the same science that led to the COVID-19 vaccines: small bits of genetic material called messenger RNA (mRNA). 

In recent years, researchers have turned to mRNA vaccines to treat different cancers, including pancreatic and breast cancers. “mRNA cancer vaccines have really benefitted from the success of COVID-19 vaccines,” says Zachary Hartman, PhD, a cancer researcher at Duke University.

But the Trump administration has been skeptical of mRNA vaccines. In August 2025, the U.S. Secretary of Health and Human Services Robert F. Kennedy Jr. halted $500 million in funding  for research into mRNA vaccines for COVID-19, bird flu, and other infectious diseases. Some cancer vaccine researchers worry this could slow progress and make it difficult to get new mRNA-based treatments approved.  

Breast cancer treatments called immunotherapies,  like checkpoint inhibitors and the HER2-targeted therapy Herceptin, use the body’s immune system to attack breast cancer cells. But these therapies don’t work for everyone, and sometimes cancer cells outsmart the immune system. mRNA vaccines could work as a new type of immunotherapy. Used alongside other immunotherapies, it could train the immune system to better recognize and attack tumors.

Every mRNA vaccine — whether for COVID-19 or cancer — carries information into the body. This information works like instructions, “teaching” the body about a certain virus or tumor. When the pathogen appears, the body recognizes it and can launch an attack.  

For COVID-19 vaccines, mRNA instructs the body to make a protein found on the COVID-19 virus called a spike protein. By making a small amount of spike protein, the immune system becomes familiar with the virus, and can recognize and fight it when a person becomes infected. 

With cancer mRNA vaccines, instead of a spike protein, vaccines carry instructions for a protein found on cancer cells. But finding which protein to target is one of the biggest challenges for developing a cancer mRNA vaccine.

Hartman says infectious diseases like COVID-19 are very different from healthy human cells, so it’s easy to find a target. But cancer cells and normal cells are very similar. 

For now, researchers are focusing on key differences they already know of, like high levels  of the HER2 protein. Researchers are also hunting for new differences, like proteins called neoantigens that form after a mutation in cancer cells.  

Vaccines that rely on mRNA likely won’t be a standalone treatment for breast cancer. They’d work alongside other therapies to keep the immune system trained and ready in case the cancer comes back. 

Several clinical trials combine mRNA vaccines with other breast cancer treatments, like the checkpoint inhibitor Keytruda (chemical name: pembrolizumab) and the chemotherapy drug Cytoxan (chemical name: cyclophosphamide). 

mRNA vaccines could also extend the lifetime of treatments or lower the chance of cancer coming back. During treatment, tumors mutate and become resistant to treatment. At Duke, Hartman and his colleague H. Kim Lyerly, MD are developing mRNA vaccines that target these mutations. The idea is that when people with breast cancer begin certain therapies, like tamoxifen or aromatase inhibitors, they also get a vaccine that protects them from the future developments of these mutations. This could help prevent the cancer from adapting to treatment over time. 

Hartman envisions a day when several vaccines exist that can treat different types of breast cancer. After someone is diagnosed and gets genetic testing, they could receive a vaccine that’s tailored to their specific type of breast cancer. But that day is still years away. 

While some clinical trials are underway, research into breast cancer mRNA vaccines is still in the early stages. One roadblock, Hartman says, is that researchers don’t know the best targets for breast cancer vaccines. “Different groups have different strategies and ideas, but I would say there’s still no consensus,” he says. 

Money is another major hurdle. Hartman says major funders want to see good results before investing a lot of money into a vaccine. Without major financing, researchers can’t go all in on mRNA cancer vaccines like they could for COVID vaccines, which was backed by the government. 

The federal government may be cooling its skepticism of mRNA vaccines. An HHS spokesperson recently told CNN that the National Institutes of Health are “focusing on high-impact areas of innovation, including mRNA-based cancer vaccines.” 

And the National Cancer Institute is raising $200 million to fund clinical trials for cancer vaccines, as first reported by The Wall Street Journal. Officials have offered few details about the initiative, but cancer researchers are hopeful. “I think this will reset the stage for vaccine interventions that many of us have been working on for many years,” Nina Bhardwaj, MD, a cancer researcher at Mount Sinai, told The Lancet Oncology.

Hartman is hopeful people will be receptive to mRNA cancer vaccines. “Patients and advocates that I’ve spoken with are excited about this and are ready to try out a vaccine,” he says, “even though the social landscape outside of cancer isn’t as favorable for vaccines.”