Seven Viruses Causing Cancer, Including HPV & Epstein-Barr Virus

Seven viruses are firmly linked to human cancers: human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), Epstein-Barr virus (EBV), human herpesvirus 8 (HHV-8/KSHV), and human T-cell lymphotropic virus type 1 (HTLV-1), and Merkel cell polyomavirus (MCV). Together they drive cervical, liver, throat, anal, lymphoma, and other cancers. Vaccines and screening prevent many of them.

The seven oncogenic viruses at a glance

Not every infection causes cancer, and these seven don't work the same way. Some insert their own genes into yours. Some keep cells dividing for decades until a tumor forms. Some inflame an organ so chronically that the tissue eventually turns malignant. What they share is time: cancer usually appears years or decades after the original infection, which is why screening and vaccination work so well.

HPV, the most common cause of viral cancer

HPV is the most common sexually transmitted infection CDC. There are dozens of types, and they fall into two camps that people constantly confuse. Low-risk types (6 and 11) cause genital warts; high-risk types (16, 18, and several others) cause cancer. The types that cause warts do not cause cancer. Most high-risk infections are silent, with no symptoms and no clinical disease.

In most cases, about 9 out of 10, HPV clears on its own within two years without ever causing harm. Genital warts, when they do show up, usually look like a small bump or a cluster of bumps in the genital area. For the full rundown on managing those, see our genital warts treatment guide.

Cervical, anal, and oropharyngeal cancers

HPV's cancer toll reaches well beyond the cervix NCI. It causes virtually all cervical cancer, over 90% of anal cancers, and about 70% of throat (oropharyngeal) cancers. Oropharyngeal cancer, tumors at the back of the throat, tonsils, and base of the tongue, has now overtaken cervical cancer as the most common HPV-related cancer in the US. HPV also drives some vulvar, vaginal, and penile cancers. For the bigger picture, see our guide to HPV and cancer.

Cervical screening is the workhorse here. Current guidance starts cervical screening at age 25 with a primary HPV test every 5 years as the preferred approach, rather than a yearly Pap American Cancer Society. Because most HPV clears within two years, an HPV test catches more precancer with fewer office visits. There's no routine HPV test for men, adolescents, or women under 30. For women, HPV is found through cervical screening rather than a general STD panel. A growing option is the self-collected HPV test, which lets you swab at home or in a clinic without a speculum exam.

Anal screening is murkier. CDC's 2021 guidance found the data insufficient to recommend routine anal cytology, even for men who have sex with men or people with HIV. That position predates the 2022 ANCHOR trial, which showed that treating anal high-grade lesions reduced anal cancer in people with HIV. Some specialty groups now suggest periodic anal Pap testing for high-risk people where high-resolution anoscopy is available, though it isn't a blanket CDC recommendation.

Treating HPV and its warts

Treatment removes warts or precancers but doesn't clear the virus. Patient-applied options include imiquimod 3.75% or 5% cream, podofilox 0.5% solution or gel, and sinecatechins 15% ointment (sinecatechins aren't recommended for immunocompromised or HIV-positive patients) CDC. In clinic, a provider may freeze warts with cryotherapy, apply TCA or BCA 80%: 90% solution, or remove them surgically by excision, curettage, laser, or electrosurgery. No single method is clearly best, and because treatment doesn't clear the virus, warts can recur. HPV testing isn't used to diagnose warts; it doesn't confirm them or guide their management. Cancer precursors are a separate problem, managed differently from warts.

Hepatitis B and Hepatitis C, liver cancer

HBV and HCV cause cancer indirectly, by inflaming the liver for years. Chronic infection scars the liver (cirrhosis), and the constant cycle of cell injury and repair eventually allows hepatocellular carcinoma, the most common type of liver cancer, to develop. Many people carry these viruses for decades without symptoms, so the first sign can be advanced liver disease.

The two diverge on prevention. Hepatitis B has a safe, effective vaccine and long-term antiviral medicines that suppress the virus and lower cancer risk. Hepatitis C has no vaccine, but it's now curable in most people with a short course of direct-acting antiviral pills, and clearing the virus before cirrhosis sets in dramatically cuts the chance of liver cancer. Both infections are often silent, and a simple blood test finds them long before the liver is damaged.

Epstein-Barr virus (EBV), lymphomas and nasopharyngeal cancer

EBV is the virus behind mononucleosis, and most adults have been infected at some point. It usually stays dormant for life. In a small subset of people, influenced by geography, genetics, and immune status, it contributes to cancers: Burkitt lymphoma and Hodgkin lymphoma (cancers of immune cells), some stomach cancers, and nasopharyngeal carcinoma (a tumor high in the throat behind the nose, far more common in parts of Asia and North Africa). There's no vaccine and no routine screening for EBV-related cancer, so the focus is recognizing symptoms early and treating the cancers when they arise.

HHV-8 (KSHV), Kaposi sarcoma

Human herpesvirus 8 causes Kaposi sarcoma, a cancer that forms purplish or brown patches and nodules on the skin and can affect internal organs. It almost always appears when the immune system is weakened, most commonly in people with untreated HIV or in transplant recipients on immunosuppressive drugs. The single most effective prevention is keeping HIV controlled with treatment; restoring the immune system often causes Kaposi lesions to shrink or disappear.

HTLV-1, adult T-cell leukemia/lymphoma

HTLV-1 infects T-cells (a type of white blood cell) and can cause adult T-cell leukemia/lymphoma, an aggressive blood cancer, in a small fraction of carriers, typically only after a very long latency, often decades. It spreads through breastfeeding, sexual contact, blood, and shared needles. There's no vaccine, so prevention rests on avoiding transmission. Most people who carry HTLV-1 never develop cancer, but those who do need specialist hematology-oncology care.

Merkel cell polyomavirus (MCV), Merkel cell carcinoma

The seventh virus is Merkel cell polyomavirus (MCV, or MCPyV), discovered in 2008. It lives harmlessly on almost everyone’s skin, but in a small number of people its DNA integrates into skin cells and drives Merkel cell carcinoma, an aggressive skin cancer. Around 80% of Merkel cell carcinomas carry the virus NCI. The cancer is rare and strongly linked to older age, fair skin, sun exposure, and a weakened immune system, which is why it shows up more often in people with HIV or on immune-suppressing medication. There is no vaccine; prevention centers on sun protection and, for higher-risk groups, watching for new or fast-growing skin nodules.

How these viruses cause cancer (the shared mechanisms)

Despite their differences, oncogenic viruses use a handful of overlapping tricks:

• Direct genetic hijacking: HPV's E6 and E7 proteins switch off the cell's tumor-suppressor brakes (the proteins that normally tell a damaged cell to stop dividing or self-destruct), letting cells multiply unchecked.
• Chronic inflammation: HBV and HCV keep the liver in a constant state of injury and repair, and each round of cell division is a fresh chance for a cancer-causing mutation.
• Immune evasion: EBV, HHV-8, and HTLV-1 hide quietly in cells for years; when immune surveillance drops (as in HIV or transplant), they can drive uncontrolled growth.
• Long latency: cancer typically appears years to decades after infection, the window that makes vaccination and screening so powerful.

What you can do: vaccines, screening, and treatment

Two of these seven are preventable by vaccine. The HPV vaccine used in the US today is Gardasil 9, which protects against nine types: 6, 11, 16, 18, 31, 33, 45, 52, and 58 CDC. Types 16 and 18 cause about 66% of cervical cancers; the five additional high-risk types add about another 15%; and types 6 and 11 cause more than 90% of genital warts. The earlier quadrivalent Gardasil covered four types and bivalent Cervarix covered two. Since 2016 only Gardasil 9 has been distributed in the US, so it guards against more cancer-causing types than the older shots.

Given at the recommended ages, the HPV vaccine can prevent more than 90% of HPV-caused cancers, and Gardasil 9 is about 98% effective against the precancers caused by HPV 16 and 18 American Cancer Society. The vaccine won't clear an infection or warts you already have, and vaccinated people still need cervical screening. The hepatitis B vaccine works the same way, preventing the chronic infection that leads to liver cancer.

For the viruses without a vaccine, prevention means controlling HIV, avoiding bloodborne and sexual transmission, treating hepatitis C to cure, and screening when guidelines call for it. Condoms give partial protection against HPV only, since the virus can infect skin a condom doesn't cover. If you're unsure where you stand, get tested, and if you've had a recent exposure, check when to test after exposure before you book.

When to see a clinician

See a clinician if you notice new genital bumps, unusual bleeding between periods or after sex, a persistent sore throat or neck lump that doesn't resolve, unexplained weight loss or swollen lymph nodes, new purplish skin patches, or yellowing of the skin or eyes. Also reach out simply to stay on schedule: to start or finish the HPV or hepatitis B vaccine series, to begin cervical screening at the recommended age, or to ask about hepatitis C testing if you've never been screened.

Keep exploring on EasySTD: STD vaccines, how and where to get tested and Hepatitis B testing.