The August 2026 press release from Merck and Moderna about a potential mRNA-based melanoma vaccine has some people asking, “How does a vaccine treat cancer?” and “What could this mean for people with or at risk of cancer?” While the headlines are exciting, this treatment option remains investigational. Given the concerns and questions around mRNA vaccines that have been licensed for prevention, such as COVID-19 and influenza, having an understanding of these potential therapeutics can be helpful. So, let’s take a closer look at the fundamentals of the science, the study behind the headlines, and the challenges that will need to be overcome.
Preventive vs. therapeutic vaccines
Most people are familiar with the historic use of vaccines to prevent infections. They understand that vaccines are given prior to exposure to an infectious disease so that the immune system is ready if the person encounters the pathogen in the future. However, we are moving into an era where vaccines may also be used as treatments — that is, after a condition has developed. Often described as therapeutic vaccines, these tools also stimulate an immune response, but that response is targeted at cancer rather than an infectious disease. Because each person’s cancer is unique, therapeutic cancer vaccines would also differ from traditional preventive vaccines because they would be personalized — that is, targeted to the individual patient’s specific cancer.
How would therapeutic mRNA vaccines work?
mRNA technology has dramatically moved us toward the promise of therapeutic vaccines. So, what are the steps needed for these personalized treatment vaccines to work?
- Analyze the genetics: Samples from the patient’s tumor and their normal cells are sequenced to identify mutations that are present only in the cancer cells. Researchers then need to figure out if these mutations can be targeted by a therapeutic vaccine. To be a good target, the mutation must result in protein fragments called neoantigens. Neoantigens are “new” proteins that result from the genetic mutations in the tumor cells. Because these “tumor-specific” proteins are different from the individual’s normal cells, the immune system responds against them.
- Use computer modeling: Scientists use computers to predict which mutations are most likely to generate neoantigens that a specific part of the immune system, T cells, will respond to. Ideally, the neoantigens are present on all of the cancer cells, not just some of them, so that any individual therapy that is designed targets all of the tumor in the person’s body.
- Make the mRNA: Once the protein target has been identified, scientists can make the mRNA that will be used in the vaccine. Two points are important here. First, the mRNA will be specific for an individual patient’s tumor cells, so it will only be produced for a single patient. Second, even if two people have the same cancer diagnosis, their tumors are likely to have different mutations and, therefore, require different mRNA therapeutic vaccines.
- Deliver the therapy: Once the therapeutic mRNA is made, it needs to be delivered to the patient. The process of designing a personalized therapeutic and delivering it to a single patient while meeting safe manufacturing standards has been shown to work in a small clinical trial. However, if this becomes a standard of care, the process will need to be fast, scalable and economically sustainable.
- Let the immune system work: Once the mRNA therapeutic has been administered, some of the recipient’s cells will take up the mRNA and temporarily produce the targeted, tumor-specific protein, enabling healthy cells to train T cells what to recognize. The immune system can then create an army of T cells able to recognize and kill any cell with the neoantigen present. Because the neoantigens are only on tumor cells, the immune system will only attack tumor cells, not healthy cells.
Ideally, immune system memory cells will remain and circulate for months or years, also decreasing the likelihood of recurrence.
The recent Phase III trial
The study behind the August headlines was a Phase III trial of an mRNA cancer vaccine, called intismeran autogene (formerly referred to as either V940 or mRNA-4157). In this trial, more than 1,100 people who had high-risk melanoma (stages II to IV) that had been surgically removed were given either a standardized, post-operative treatment, called pembrolizumab, plus placebo, or pembrolizumab combined with a personalized mRNA vaccine. Pembrolizumab, used to treat many cancers, is a monoclonal antibody that restores antitumor immune responses, which are often inhibited by tumor cells.
Over a study period of up to seven years, researchers measured how long people remained free of melanoma (recurrence-free survival), as well as how long they went without cancer spreading to distant parts of the body (distant metastasis-free survival). The initial press release from the pharmaceutical companies shares that the trial met its recurrence-free survival and distant metastasis-free survival endpoints, but it did not disclose the data.
Data from a Phase IIb trial of 157 people demonstrated that those who received the therapeutic vaccine combined with pembrolizumab had improved recurrence-free survival, with an almost 50% reduction in recurrence or death, and a 59% reduction in distant metastasis or death compared with those who received pembrolizumab and placebo injections. The data showed a greater number and more diverse repertoire of T cells (clonality), with the latter more likely in patients who remained recurrence free during the study. However, while the results were favorable, the small sample size and some large confidence intervals limit the conclusions that can be drawn from this study. As such, the Phase III trial data will offer additional understanding of the potential this treatment offers patients. Full data review for the Phase III trial, including a peer-reviewed publication, are not yet available.
Looking ahead: Challenges to overcome
The biological rationale and early data related to this technology are compelling. However, as with any scientific progress, many questions and considerations still need to be addressed. For example, when is the optimal time to administer a therapeutic vaccine? Should surgery occur first, as happened in the melanoma trial? Are combined therapies required (e.g., coadministration with a drug like pembrolizumab)? How long do the effects last (i.e., how long-lived are the memory cells generated during treatment and how long will they prevent recurrence)? How can therapeutics with individualized aspects of production be scaled? How will regulators review these types of personalized products? Which types of cancer are most likely to be a good fit for this technology?
While the potential offered by these types of therapeutics is exciting for affected patients, their families and their treatment teams, we also know that new technologies can be met with questions and uncertainty, particularly as ideas spread among the general population. For this reason, it can be helpful to follow the developments and be prepared to answer questions before they come into the exam room.
We already have two preventive vaccines that can decrease a person’s chance of developing some types of cancer. The hepatitis B vaccine prevents liver cancer, and the human papillomavirus (HPV) vaccine prevents cervical and other cancers associated with long-term HPV infections. Both lack optimal uptake despite their incredible safety and effectiveness records. Helping families realize the potential already in front of us and discussing the benefits of prevention over treatment can go a long way in walking this new road toward therapeutic vaccines together when the time comes.
The August 2026 press release from Merck and Moderna about a potential mRNA-based melanoma vaccine has some people asking, “How does a vaccine treat cancer?” and “What could this mean for people with or at risk of cancer?” While the headlines are exciting, this treatment option remains investigational. Given the concerns and questions around mRNA vaccines that have been licensed for prevention, such as COVID-19 and influenza, having an understanding of these potential therapeutics can be helpful. So, let’s take a closer look at the fundamentals of the science, the study behind the headlines, and the challenges that will need to be overcome.
Preventive vs. therapeutic vaccines
Most people are familiar with the historic use of vaccines to prevent infections. They understand that vaccines are given prior to exposure to an infectious disease so that the immune system is ready if the person encounters the pathogen in the future. However, we are moving into an era where vaccines may also be used as treatments — that is, after a condition has developed. Often described as therapeutic vaccines, these tools also stimulate an immune response, but that response is targeted at cancer rather than an infectious disease. Because each person’s cancer is unique, therapeutic cancer vaccines would also differ from traditional preventive vaccines because they would be personalized — that is, targeted to the individual patient’s specific cancer.
How would therapeutic mRNA vaccines work?
mRNA technology has dramatically moved us toward the promise of therapeutic vaccines. So, what are the steps needed for these personalized treatment vaccines to work?
- Analyze the genetics: Samples from the patient’s tumor and their normal cells are sequenced to identify mutations that are present only in the cancer cells. Researchers then need to figure out if these mutations can be targeted by a therapeutic vaccine. To be a good target, the mutation must result in protein fragments called neoantigens. Neoantigens are “new” proteins that result from the genetic mutations in the tumor cells. Because these “tumor-specific” proteins are different from the individual’s normal cells, the immune system responds against them.
- Use computer modeling: Scientists use computers to predict which mutations are most likely to generate neoantigens that a specific part of the immune system, T cells, will respond to. Ideally, the neoantigens are present on all of the cancer cells, not just some of them, so that any individual therapy that is designed targets all of the tumor in the person’s body.
- Make the mRNA: Once the protein target has been identified, scientists can make the mRNA that will be used in the vaccine. Two points are important here. First, the mRNA will be specific for an individual patient’s tumor cells, so it will only be produced for a single patient. Second, even if two people have the same cancer diagnosis, their tumors are likely to have different mutations and, therefore, require different mRNA therapeutic vaccines.
- Deliver the therapy: Once the therapeutic mRNA is made, it needs to be delivered to the patient. The process of designing a personalized therapeutic and delivering it to a single patient while meeting safe manufacturing standards has been shown to work in a small clinical trial. However, if this becomes a standard of care, the process will need to be fast, scalable and economically sustainable.
- Let the immune system work: Once the mRNA therapeutic has been administered, some of the recipient’s cells will take up the mRNA and temporarily produce the targeted, tumor-specific protein, enabling healthy cells to train T cells what to recognize. The immune system can then create an army of T cells able to recognize and kill any cell with the neoantigen present. Because the neoantigens are only on tumor cells, the immune system will only attack tumor cells, not healthy cells.
Ideally, immune system memory cells will remain and circulate for months or years, also decreasing the likelihood of recurrence.
The recent Phase III trial
The study behind the August headlines was a Phase III trial of an mRNA cancer vaccine, called intismeran autogene (formerly referred to as either V940 or mRNA-4157). In this trial, more than 1,100 people who had high-risk melanoma (stages II to IV) that had been surgically removed were given either a standardized, post-operative treatment, called pembrolizumab, plus placebo, or pembrolizumab combined with a personalized mRNA vaccine. Pembrolizumab, used to treat many cancers, is a monoclonal antibody that restores antitumor immune responses, which are often inhibited by tumor cells.
Over a study period of up to seven years, researchers measured how long people remained free of melanoma (recurrence-free survival), as well as how long they went without cancer spreading to distant parts of the body (distant metastasis-free survival). The initial press release from the pharmaceutical companies shares that the trial met its recurrence-free survival and distant metastasis-free survival endpoints, but it did not disclose the data.
Data from a Phase IIb trial of 157 people demonstrated that those who received the therapeutic vaccine combined with pembrolizumab had improved recurrence-free survival, with an almost 50% reduction in recurrence or death, and a 59% reduction in distant metastasis or death compared with those who received pembrolizumab and placebo injections. The data showed a greater number and more diverse repertoire of T cells (clonality), with the latter more likely in patients who remained recurrence free during the study. However, while the results were favorable, the small sample size and some large confidence intervals limit the conclusions that can be drawn from this study. As such, the Phase III trial data will offer additional understanding of the potential this treatment offers patients. Full data review for the Phase III trial, including a peer-reviewed publication, are not yet available.
Looking ahead: Challenges to overcome
The biological rationale and early data related to this technology are compelling. However, as with any scientific progress, many questions and considerations still need to be addressed. For example, when is the optimal time to administer a therapeutic vaccine? Should surgery occur first, as happened in the melanoma trial? Are combined therapies required (e.g., coadministration with a drug like pembrolizumab)? How long do the effects last (i.e., how long-lived are the memory cells generated during treatment and how long will they prevent recurrence)? How can therapeutics with individualized aspects of production be scaled? How will regulators review these types of personalized products? Which types of cancer are most likely to be a good fit for this technology?
While the potential offered by these types of therapeutics is exciting for affected patients, their families and their treatment teams, we also know that new technologies can be met with questions and uncertainty, particularly as ideas spread among the general population. For this reason, it can be helpful to follow the developments and be prepared to answer questions before they come into the exam room.
We already have two preventive vaccines that can decrease a person’s chance of developing some types of cancer. The hepatitis B vaccine prevents liver cancer, and the human papillomavirus (HPV) vaccine prevents cervical and other cancers associated with long-term HPV infections. Both lack optimal uptake despite their incredible safety and effectiveness records. Helping families realize the potential already in front of us and discussing the benefits of prevention over treatment can go a long way in walking this new road toward therapeutic vaccines together when the time comes.