Viruses and cancer

Infection with certain viruses can sometimes cause cancer. Some of these infections can be prevented by vaccines and therefore the chance of getting certain types of cancer can be minimised. Dr Sze Wai Chan, a medical oncologist, talks us through some of the common viruses that are linked to cancer.

What are viruses?

Viruses are tiny organisms containing genetic material – deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) – and are covered by a protein shell. When cancer causing viruses infect a living cell, the virus DNA or RNA enters and disrupts the host cell’s genes and this in turn can cause the cell to become cancerous (multiplying or growing abnormally).

Human papilloma viruses (HPV) 

Infection with HPV is very common. HPVs are spread by contact (touch) and sex, including vaginal, anal, and oral sex. Most sexually active people are infected with one or more HPV subtypes at some point in their lives.

HPVs are classified as low-risk or high-risk subtypes. Low-risk HPVs rarely cause cancer but usually cause warts (papilloma); these are found either on the skin or mucous membranes (e.g. vagina, anus, mouth, and throat). High-risk HPVs can cause cancer; the common ones are HPV types 16 and 18.

There is no effective treatment for HPV but our immunity is usually able to clear the infection on its own. But sometimes, the infection doesn’t go away. Chronic, or long-lasting infection, especially when it’s caused by certain high-risk HPV subtypes, can cause cancer over time.

While HPV infections are very common, cancer caused by HPV is not. Most people infected with HPVs will not develop a cancer related to the infection.

HPV infections and cancers:

1. Cervix cancer

According to the South African National Cancer Registry of 2011, cervix cancer is the third most common cancer in females. The main cause of cervix cancer is HPV infections. Cervical cancer is preventable with vaccines and regular screening tests.

Pap smears are useful for cervical cancer screenings. It is done by brushing off or scraping off a thin layer of cells from the cervix. The Pap smear allows us to see (under the microscope) pre-cancerous changes in cells of the cervix that might be caused by HPV infection. These pre-cancerous cells can then be destroyed or removed surgically, thus preventing cervical cancer from developing.

HPV testing checks for the HPV  virus and it can be done at the time of the Pap smear. Combining a Pap smear with HPV testing will give us more information to screen for cervical cancer.

2. Head and neck cancers (mouth and throat)

Most head and neck cancers are caused by cigarette smoking and alcohol consumption.  However, HPVs can cause head and neck cancers, especially in the base of the tongue and tonsils. HPV-related head and neck cancers are associated with younger age at diagnosis, male preponderance, better prognosis and response to therapy.

3. Other cancers

HPVs can cause cancers of the penis, anus, vagina, and vulva. There’s no standard screening test for these cancers. HPV causes nearly all squamous cell cancer of the anus in both men and women. Both penis and anus cancers are more common in people with HIV and in men who have sex with other men.

HPV vaccines

HPV vaccines (Gardasil and Cervarix) are available and can be used to prevent infection with certain types of HPV. All HPV vaccines help prevent infections with HPV types 16 and 18, and some protect against other types, including types that can cause anal and genital warts.

HPV vaccines are approved for use in males and females. They are used to prevent HPV infection and not to treat an existing infection. The vaccines should be given at or before age 11 or 12, in a series of shots, and are most effective when given before a person becomes sexually active.

Epstein-Barr virus (EBV)

EBV is best known for causing infectious mononucleosis, often called the “kissing disease.” In addition to kissing, EBV can be passed from person to person by coughing, sneezing, or by sharing drinks or utensils. Most people are infected with EBV by the end of their teenage years, although not everyone develops the symptoms.

EBV infection is lifelong. There are  no medicines or treatment to get rid of EBV, and there are no vaccines to prevent it, as EBV infection usually  does not cause serious problems in   most people.

In some cases, EBV infection can increase a person’s risk of getting nasopharyngeal cancer. EBV infects and stays in certain white blood cells in the body, called B lymphocytes or called B cells, and can cause an aggressive lymphoma, called Burkitt’s lymphoma. It may also be linked to Hodgkin’s lymphoma. EBV-related cancers are more common in Africa and Southeast Asia.

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

Both HBV and HCV cause viral hepatitis, a type of liver infection. Most people recover completely from HBV infection. However, some patients cannot remove HBV or HCV from the body, and a prolonged (chronic) infection ensues. This damages the liver over time, and increases the risk of liver cancer. Liver cancer caused by chronic HBV infection is very common in SA.

HBV and HCV are spread from person to person in much the same way as HIV – through sharing needles (during injection drug use), unprotected sex, or childbirth and occasionally from blood transfusions (rare nowadays because donated blood is screened for infectious agents such as HBV, HCV and HIV).

Both hepatitis B and C infections can be treated. Treatment cannot cure the disease but they can lower the risk of liver damage and therefore, lower the risk of liver cancer.

There is a vaccine to prevent HBV infection, but none for HCV. HBV vaccine is recommended for all children. It’s also recommended for adults who are at risk of exposure, such as people infected with HIV, men who have sex with men, injection drug users, people in certain group homes, people with certain medical conditions and healthcare workers.

Human herpesvirus 8 (HHV-8)

HHV-8, also known as Kaposi sarcoma-associated herpesvirus (KSHV), causes Kaposi sarcoma (KS). KS is a slow-growing cancer of blood vessels and appears as purple lesions just underneath the skin. KS can also appear in the mucosa (e.g. palate, respiratory airways and gastrointestinal tracts).

HHV-8 is transmitted through sex and seems to spread through blood and saliva as well. HHV-8 infection is lifelong but it does not appear to cause disease in healthy people. Having a weakened immune system – such as HIV infection or immune suppression after an organ transplant – appears to be a risk factor for developing KS.

HHV-8 infection has also been linked to primary effusion lymphoma(PEL) and Castleman disease (CD) (overgrowth of lymph nodes). Both conditions are often related to HIV infections.

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

HTLV-1 has been linked with a type of leukemia/lymphoma, called Adult T-cell leukemia/lymphoma (ATL). This cancer is found mostly in Japan, the Caribbean, central Africa, parts of South America, and in some immigrant groups in the Western countries.

HTLV-1 is spread via unprotected sex or sharing injection needles. Mothers infected with HTLV-1 can also pass on the virus to their children via breastfeeding.

Merkel cell polyomavirus (MCV)

MCV is associated with an aggressive type of skin cancer, called Merkel cell carcinoma. Most people are infected with MCV at some point (often in childhood), and it usually causes no symptoms. But in a few people with this infection, the virus can lead to Merkel cell cancer.

Human immunodeficiency virus (HIV)

HIV infection does not cause cancer per se, but many viruses are spreading in similar ways like HIV, such as HBV, HPV and HHV-8. Therefore, the incidence of cancers relating to these viruses are higher in HIV infected patients.