Most viruses are too tiny to see with a microscope. They include a few DNA or RNA genes wrapped in protein. To proliferate, a virus must penetrate a living cell and take over its machinery. Some viruses inject their DNA (or RNA) into the host cell’s. DNA or RNA that changes a cell’s genes can cause cancer.

Each virus infects a certain sort of body cell. (Cold viruses affect only nose and throat cells.)

Viruses cause human cancer. Our expanding understanding of viruses as cancer causes has led to the creation of vaccinations. These vaccines can only prevent cancer if given before exposure.

Human Papilloma Viruses (HPVs)

HPVs are a category of 150 viruses. Some cause papilloma, or warts. Some HPV only develop on skin, whereas others grow in the mouth, throat, or vagina.

Contact spreads all HPV kinds (touch). Sexual contact spreads over 40 strains of HPV. Most sexually active persons have one or more of these HPV types. At least 12 cause cancer.

Cancer caused by HPV is rare. Most HPV-infected persons won’t get cancer. Long-term infections with high-risk HPV can cause cancer.

HPV and Cervical Cancer

Mucous membrane HPV infections can create genital warts, but they’re normally symptomless. HPV can only be treated by removing or destroying contaminated cells. Most people’s immune systems control or eliminate HPV infections. See HPV and HPV Testing.

Several forms of HPV cause cervical cancer, the second most prevalent malignancy in women. The Pap test has made cervical cancer less common in the U.S. This test can detect cervical pre-cancer caused by HPV. Pre-cancerous cells can be eliminated or eradicated. It prevents cancer.

Doctors can now test for HPV as part of cervical cancer screening to determine risk. Nearly of cervical cancer patients test positive for HPV. Doctors can test cervix-bearing patients for HPV, but there’s no therapy. Vaccines can prevent it. HPV-caused abnormal cell growth can be eliminated or killed.

HPV and other cancers

HPV causes penis, anus, vagina, vulva, mouth, and throat cancers.

HPV and smoking may increase cancer risk. Other genital infections may raise HPV’s cancer risk.

You can get more details in HPV and Cancer.

Vaccines against HPV

Vaccines protect children and young people against cancer-causing HPV strains. HPV vaccine prevents 90% of HPV malignancies. These vaccines are licensed for females and males and are injected (shots).

Vaccines only prevent HPV infection; they don’t stop or treat an existing infection. Before sexual activity, the immunization series is most effective (has sex with another person).

Recommendations for HPV vaccination

HPV vaccine works best for 9-12-year-old boys and girls.
Children and young adults ages 13 to 26 who haven’t been vaccinated or haven’t gotten all their doses should get it soon. Young adults aren’t as cancer-resistant as youngsters and teens.

HPV vaccination for those above 26.
Read about HPV vaccines.

Epstein-Barr virus (EBV)

herpes virus EBV It causes infectious mononucleosis, or “mono” EBV can be spread by coughing, sneezing, or sharing drinking or eating utensils. Most Americans are infected with EBV by late adolescence, although not everyone has mono.

EBV infection is lifelong, however most people have no symptoms after a few weeks. EBV infects B lymphocytes in the body (also called B cells). There are no medicines or vaccines to treat or prevent EBV, but most people don’t have serious problems from it.

EBV infection raises the risk of nasopharyngeal carcinoma and Burkitt lymphoma. Hodgkin lymphoma and stomach cancer may be connected. Africa and Southeast Asia have more EBV-related cancers. Few EBV-infected people acquire malignancies.

Hepatitis B virus (HBV) and hepatitis C virus (HCV)

Viral hepatitis is caused by HBV and HCV. Other viruses cause hepatitis (hepatitis A virus, for example), but only HBV and HCV cause persistent infections that increase liver cancer risk. In the U.S., HBV or HCV infection causes less than half of liver cancers. In some other countries, viral hepatitis and liver cancer are more common. Some study links long-term HCV infection to non-Hodgkin lymphoma.

HBV and HCV are shared like HIV, through sharing needles, unprotected intercourse, or delivery. They can be spread by blood transfusions, but this is unusual in the US because donated blood is checked.

HBV causes flu-like symptoms and jaundice more often than HIV (yellowing of the eyes and skin). Most adults recover from HBV within months. Children are more likely than adults to develop persistent HBV infections. Chronic HBV infections cause liver cancer.

HCV causes fewer symptoms than HBV, but chronic infection might lead to liver damage or malignancy. Most Americans with chronic HCV don’t know they have it. To assist discover unknown infections, the CDC advises that all adults 18 and older get tested for HCV at least once, and some groups more regularly. Visit for a detailed list of who should get HCV tested and how often.

Once an infection is found, therapy and prevention can lessen liver damage and cancer risk. Drugs can treat hepatitis B and C. Chronic hepatitis C can be cured with a few months of medication treatment. Several medications can treat chronic hepatitis B. They don’t cure the condition, but they can reduce liver damage and cancer risk.

HCV does not have a vaccination. All U.S. children should have the HBV vaccine. It’s also advised for elderly persons at risk of HBV exposure. This includes HIV-positive people, men who have intercourse with men, injectable drug users, people in specific group homes, and others. Visit for a complete list of who should get the HBV vaccine.


HIV, which causes AIDS, doesn’t cause malignancies directly. HIV infection increases a person’s risk of cancer, especially virus-linked cancers.

Semen, vaginal fluids, blood, and breast milk can spread HIV. Spread via:

Oral, vaginal, or anal unprotected intercourse with an HIV-positive individual
Injections with HIV-infected needles
Prenatal/perinatal (during birth) HIV-exposed babies
HIV-positive women breastfeeding
HIV-contaminated transfusions (the risk of HIV from a transfusion is less than 1 in a million in the United States due to blood testing and donor screening)
HIV-positive transplants (donors are now tested for HIV)
Penetrating injuries (typically needle sticks) in health care personnel caring for HIV-infected patients or handling their blood.
HIV isn’t spread through insects, water, casual touch, or sharing dishes, restrooms, kitchens, phones, or computers. No saliva, tears, or sweat spread it.

HIV kills helper T-cells, weakening the immune system. This could let HPV and other cancer-causing viruses grow.

Many scientists believe the immune system helps attack and destroy cancer cells. Weak immune systems can let cancer cells grow into life-threatening tumors.

HIV is connected to Kaposi sarcoma and cervical cancer. It’s associated to non-Hodgkin lymphoma, especially CNS lymphoma.

Other cancers more likely in HIV-positive patients include:

Oral cancers
Skin cancer
HIV may also increase the risk of developing less common cancers.

Because HIV infection often has no symptoms for years, a person can have it without knowing. The CDC recommends HIV testing for everyone 13 to 64 as part of normal care.

HIV isn’t preventable. You can minimize your risk by not having unprotected intercourse or sharing needles with an HIV-positive person. Injection drug users and persons whose partners have HIV can reduce their risk of HIV infection by taking a daily tablet.

Anti-HIV medications can help HIV-positive persons halt immune system deterioration, which may lessen cancer risk.

Human herpes virus 8 (HHV-8)

Nearly all Kaposi sarcoma tumors include HHV-8, also called KSHV (KS). KS is an uncommon, slow-growing malignancy with reddish-purple or blue-brown tumors. HHV-8 infects KS blood and lymph vessel cells. Infection causes them split too much and live longer. These alterations can cause cancer.

HHV-8 is spread by intercourse, blood, and saliva. Fewer than 10% of Americans have this virus, according to studies.

As with other herpes viruses, HHV-8 infection is lifelong, but it seldom causes disease in healthy persons. HHV-8 infects many more people than ever get KS, so other causes must be involved. A compromised immune system may be one. In the US, practically all KS patients have impaired immune systems from HIV or organ transplants.

KS was infrequent in the US until AIDS patients contracted it in the 1980s. Since the early 1990s, fewer Americans had KS due to better HIV treatment.

Kaposi Sarcoma (KS)

HHV-8 is connected to rare blood malignancies such primary effusion lymphoma. Many persons with multicentric Castleman disease, an enlargement of lymph nodes that often becomes lymphoma, have the virus (lymphoma). HHV-8’s role in these disorders needs more study.

Human T-lymphotrophic virus-1 (HTLV-1)

Adult T-cell leukemia/lymphoma is connected to HTLV-1 (ATL). This cancer is common in southern Japan, the Caribbean, central Africa, South America, and several southeastern U.S. immigrant communities.

This virus can cause various health concerns, however many HTLV-1 patients don’t have them.

Retroviruses include HTLV-1. RNA is these viruses’ genetic code, not DNA. They must convert RNA genes to DNA to reproduce. Some of the additional DNA genes can become part of the virus-infected cell’s chromosomes. This can alter cell growth and division, leading to cancer.

HTLV-1 is a retrovirus like HIV. HTLV-1 doesn’t cause AIDS. HTLV-1 is disseminated in people by unprotected sex with an infected partner or injection with a discarded needle. HTLV-1-infected mothers can spread the virus to their children if they breastfeed.

HTLV-1 is uncommon in the US. HTLV-1 infects less than 1% of Americans, but the rate is substantially greater in high-risk groups (such as injection drug users). Since 1988, every U.S. blood has been HTLV-1-screened. This has lowered the risk of infection through transfusion and helped curb HTLV-1 spread.

A person infected with HTLV-1 has a 5% chance of acquiring ATL, usually after a lengthy time without symptoms (20 or more years).

Polyomavirus Merkel (MCV)

Merkel cell carcinoma samples had MCV in 2008. MCV infects most people (typically in childhood) but seldom causes symptoms. In a few people, this virus can alter cell DNA, causing Merkel cell cancer. This infection may cause nearly all Merkel cell malignancies.

This virus has been detected in normal skin and saliva, but its mode of transmission is unknown.

Unproven or unknown human cancer viruses

SV40 (SV40)

SV40 infects monkeys. SV40 infected certain polio vaccines manufactured from monkey cells between 1955 and 1963.

Older research revealed that SV40 infection may raise the incidence of mesothelioma, brain tumors, bone malignancies, and lymphomas. Older studies’ accuracy is questioned.

Scientists found that SV40-infected hamsters developed mesotheliomas. SV40 can make lab-grown mouse cells malignant, say researchers.

Other studies have detected SV40-like DNA fragments in cancer biopsies. Similar fragments can also be discovered in human tissues without cancer.

The largest investigations on this issue have not identified an elevated risk for mesothelioma or other cancers in people who took tainted polio immunizations as youngsters. Recent lung mesothelioma instances have risen primarily among males 75 and older, who would not have received the vaccine. Mesothelioma rates have gone decreased among those who had the immunization. Even while women are just as likely to get the vaccination, more men are diagnosed with mesothelioma.

SV40 causes cancer in certain lab animals, but research suggests it doesn’t in humans.