Viruses and Cancer

During the past year, COVID-19 has taught us to appreciate the significant impact that viruses can have on our health and well-being.  Human health can be impacted by many different types of virus with some causing diseases such as the common cold (rhinovirus), influenza, rabies and poliomyelitis.  

The potential impact of viruses can be avoided or minimised by a person’s general good health, strength of the immune system, favourable genetics, avoidance of sources of infection and immunisation.  However, on rare occasions, viral infections have been shown to lead to cancer.

Oncogenic viruses (viruses that can cause cancer) act by integration of their DNA into the host cell.  This can lead to the development of cancer in a variety of ways, such as when these viral oncogenic genes impair the functioning of two families of tumour suppressor proteins, namely p53 and retinoblastoma proteins (Rb).  

P53 and Rb are involved in controlling the cell division cycle by allowing time for damaged or altered DNA to the repaired and, if repair is not possible, to initiate programmed cell death or apoptosis.  Interference or disabling p53 and/or Rb can instigate uncontrolled cell division leading to cancer.  In addition, the cancer may arise through the action of the oncogenic virus leading to the suppression or disruption of the immune system or by the viral infection causing long-term or chronic inflammation in the susceptible organ or tissue.

In 2002 the World Health Organisation estimated that about 18% of human cancers were caused by viral infections and with the majority attributed to only seven viruses.  

1. Human papillomavirus (HPV) – there are more than 200 types of HPV, with 14 high-risk types including HPV 16 and HPV 18.  Transmission is through skin-to-skin contact and has been shown to cause cancer of the cervix, vagina, vulva, penis, anus and oropharynx.  Supporters like you contributed to the seed funding for Professor Ian Frazer’s development of a cervical cancer vaccine which protects against HPV 16 and HPV 18. Thanks to a national immunisation program, Australia is set to be the first country to effectively eliminate the disease.
2. Epstein-Barr virus (EPV) – this herpes type virus is usually associated with mononucleosis or glandular fever and is spread through bodily fluids such as saliva and blood.  EPV can lead to mutations that contribute to certain rare cancers, such as Burkitt’s lymphoma, nasopharyngeal cancer and Hodgkin’s lymphoma.  
3. Hepatitis B virus (HBV) – spread through sharing bodily fluids.  Chronic HBV infection leads to liver inflammation and damage that are risk factors for liver cancer. 
4. Hepatitis C virus (HCV) – less likely to show symptoms than HBV but with a higher incidence of chronic infection.  HCV is associated with liver inflammation and damage which are risk factors for liver cancer.
5. Human herpes virus 8 (HHV-8) – transmitted through saliva.  Infections are rare and can particularly impact on people with a weakened immune system.  HHV-8 has been associated with Kaposi sarcoma.  
6. Human T-lymphotrophic virus (HTLV) – a retrovirus that is spread through blood transfers, breast milk and semen.  There are no symptoms but HTLV is associated with acute T-cell leukaemia/lymphoma.
7. Merkel Cell polyomavirus (MCV) – potential skin-to-skin transmission with no symptoms.  MCV is associated with Merkel Cell carcinoma, a rare type of skin cancer. 

The prevention of viral cancers has found success in utilising vaccines to stimulate the body’s immune system to block infection.  The Hepatitis B vaccine was the first vaccine recognised for its ability to help reduce the risk of liver cancer.  The HPV vaccine (Gardasil) was approved by the FDA in 2006 to prevent cervical cancer in adolescent girls.  Hundreds of millions of doses of Gardasil have been used in many countries around the world in preventative campaigns.  Subsequent research has shown it to be effective in reducing the incidence of a number of other genital cancers in both boys and girls.  The current version, Gardasil 9, protects against nine types of HPV including seven of those posing the highest risk.

Apart from vaccines the prevention of viral infections is best achieved through good hygiene, hand washing, not sharing personal items, using barrier protection during sexual activity and screening for viral infections such as HCV. 

This article was written by Dr Ian Brown, ACRF Chief Scientific Officer.