What Is a Cancer Vaccine? Preventive vs. Therapeutic Vaccines Explained

"Cancer vaccine" actually describes two quite different tools that share a name but not much else. Preventive cancer vaccines — like the HPV and hepatitis B vaccines — are given to healthy people to block the viral infections that can eventually cause cancer, and they are among the most successful cancer-prevention interventions in medicine. Therapeutic cancer vaccines, by contrast, are given to people who already have cancer, and try to teach the immune system to recognize and attack tumor cells that are already present. This article walks through both categories, introduces the one therapeutic cancer vaccine currently FDA-approved (sipuleucel-T, or Provenge), explains how vaccines differ from checkpoint inhibitors and CAR-T therapy, and looks at the newer personalized and mRNA-based vaccines now moving through clinical trials.

Two Very Different Kinds of Cancer Vaccine

The National Cancer Institute (NCI) groups cancer vaccines into two categories based on when they're given and what they're meant to do. Prevention vaccines are given to people who are cancer-free, and they work exactly like a flu or measles shot: they train the immune system to recognize a specific virus, so that virus never gets the chance to trigger cancer-causing changes in cells years later. Treatment (therapeutic) vaccines go to people already diagnosed with cancer. Instead of preventing infection, they try to get the immune system to recognize proteins on existing tumor cells as a threat and mount an attack against them. Keeping this distinction in mind is the single most useful thing a newcomer can do — "cancer vaccine" news can mean either a well-established prevention tool or an experimental treatment still being tested.

Preventive Vaccines: Stopping Cancer Before It Starts

The clearest cancer-vaccine success story is the HPV vaccine. Human papillomavirus (HPV) causes nearly all cervical cancers and a substantial share of anal, oropharyngeal (throat), penile, vulvar, and vaginal cancers. Gardasil 9, the vaccine used in the U.S. today, targets nine HPV types responsible for most of these cancers plus genital warts, and is routinely recommended starting at ages 11–12. The real-world results have been genuinely striking: the CDC reports an 88% drop in infections with cancer-causing HPV types among vaccinated teen girls, and its HPV-IMPACT surveillance data show cervical precancers falling by roughly 80% among screened women ages 20–24 between 2008 and 2022. A 2024 analysis reported by outlets covering a JAMA-based study found cervical cancer deaths among young U.S. women dropped 62% over the past decade, a trend researchers attribute largely to vaccination. It's rare in medicine to see a prevention tool work this well this fast.

The hepatitis B vaccine tells a similar, longer-running story for liver cancer. Chronic hepatitis B infection is a leading cause of hepatocellular carcinoma (the most common form of liver cancer) worldwide. When Taiwan launched universal infant hepatitis B vaccination in 1984, researchers tracked both infection rates and cancer outcomes over the following decade. A landmark 1997 study in the New England Journal of Medicine found that hepatocellular carcinoma incidence in children fell substantially across the vaccination era, alongside a large drop in chronic HBV infection rates. It remains one of the strongest pieces of evidence that a vaccine against an infection can, years later, meaningfully cut cancer rates in a population.

Therapeutic Vaccines: Training the Immune System Against Existing Cancer

Therapeutic cancer vaccines are a different and much harder problem: getting the immune system to recognize a tumor that has already learned to evade it. The one FDA-approved example is sipuleucel-T (Provenge), approved in April 2010 for men with metastatic castration-resistant prostate cancer who have few or no symptoms. It's made individually for each patient: immune cells are collected from the patient's blood, exposed in a lab to a protein found on most prostate cancer cells combined with an immune-stimulating factor, and then infused back into the patient to (in theory) prime the immune system to attack the cancer. It was a genuine milestone — the first therapeutic cancer vaccine ever approved — but it illustrates how modest the benefit can be even when a vaccine works: it extends median survival by a few months rather than producing dramatic tumor shrinkage, and it isn't used to treat cancer the way chemotherapy is.

How Cancer Vaccines Differ From Checkpoint Inhibitors and CAR-T

It helps to place cancer vaccines alongside the other major immunotherapy approaches. Checkpoint inhibitors (drugs like pembrolizumab/Keytruda or nivolumab/Opdivo) don't teach the immune system anything new — they release molecular "brakes" that tumors exploit to hide from immune cells that can already recognize them. CAR-T cell therapy goes further: it removes a patient's T cells, genetically engineers them to carry a receptor that targets a specific cancer protein, and infuses them back in large numbers, essentially building a custom weapon outside the body. Cancer vaccines take a third route entirely — rather than releasing brakes or engineering cells externally, they try to get the patient's own immune system to learn to recognize cancer on its own, the way it learns to recognize a virus. That's a more ambitious goal, and it's part of why therapeutic vaccines have had a harder path to success than checkpoint inhibitors or CAR-T.

The Next Wave: Personalized and mRNA Cancer Vaccines

The most encouraging recent development in this field is personalized, neoantigen-based mRNA vaccines. Moderna and Merck's intismeran autogene (formerly mRNA-4157/V940) is custom-built for each patient from their own tumor's mutations, encoding dozens of patient-specific neoantigens, and is given alongside pembrolizumab in people with surgically removed high-risk melanoma. In the Phase 2b KEYNOTE-942 trial, 5-year follow-up data presented in 2026 showed the combination substantially cut the risk of recurrence or death and the risk of distant metastasis or death compared with pembrolizumab alone — a genuinely notable result for a therapeutic vaccine. In August 2026, Merck and Moderna announced that the larger, confirmatory Phase 3 INTerpath-001 trial also met its primary endpoints, and the companies have said they plan to engage regulators about a filing. It is important to be precise here: as of this writing, intismeran autogene is investigational and not yet FDA-approved; a positive Phase 3 readout is a major step, not a finish line. Other personalized neoantigen and mRNA vaccine candidates are in earlier-stage trials across melanoma, pancreatic, lung, and other cancers, with similarly investigational status.

Why Therapeutic Cancer Vaccines Have Struggled

It's worth being honest about the field's track record. For decades, therapeutic cancer vaccines produced far more clinical trial failures than successes — many candidates that looked promising in early studies failed to show a survival benefit in larger, randomized trials, and sipuleucel-T remained the lone FDA-approved example for well over a decade. Tumors are genetically unstable and actively suppress immune responses against themselves, patients' immune systems are often weakened by prior cancer treatment, and finding tumor targets that are both cancer-specific and immunologically visible has proven difficult. The personalized, neoantigen-driven approach — building a vaccine from a patient's own tumor mutations rather than a one-size-fits-all target, and pairing it with a checkpoint inhibitor — is the field's best current answer to those obstacles, but it remains to be seen how many candidates will clear the bar that so many earlier vaccines could not.

Bottom Line

Preventive cancer vaccines — HPV and hepatitis B — are proven, approved, and already measurably reducing cancer deaths; they belong in the same category as any other highly effective vaccination. Therapeutic cancer vaccines are a different story: one, sipuleucel-T, is FDA-approved with a modest benefit, and the field has a long history of trial failures behind it. The personalized mRNA vaccines now succeeding in Phase 3 melanoma trials are the most promising development therapeutic vaccines have seen in years, but they are still investigational, not yet approved, and their eventual role in cancer care is still being written.