Infections

An estimated 3.3% of cancer cases in Australia and New Zealand are attributable to infections.⁸² Globally, an estimated 16.1% of new cancers are attributed to infections, however estimates vary greatly between regions.⁸²

A 2012 IARC Monograph on biological agents identified a number of different agents that cause cancers.⁷ Human papillomavirus, Helicobacter pylori, and hepatitis B and C viruses were identified as the principal infectious agents in the World Cancer Report 2008, accounting internationally for 6.1%, 5.4% and 4.3% of all cancer cases respectively⁸³ and 1.9 million cancer cases worldwide.⁸²

Human papillomavirus and cancer

Human papillomavirus (HPV) is a sexually transmitted virus. WHO has reported that HPV is responsible for 235,000 cancer deaths each year.⁴ The IARC Monograph on biological agents classified certain types of HPV as Group 1 carcinogens, and reported that certain types of the virus cause cervical cancer, vulval cancer, vaginal cancer, penile cancer, anal cancer, oral cavity cancer, oropharyngeal cancer and tonsil cancer.⁷ HPV is estimated to cause 100% of cervical cancer cases, 90% of anal cancers and 40% of external genitalia cancers.⁸⁴ The IARC evidence also supports an association between HPV and laryngeal cancer.⁷

Hepatitis B, hepatitis C and cancer

Hepatitis B and C viruses (HBV and HCV) are infections of the liver, transmitted via contact with blood or body fluids.⁸⁵,⁸⁶ The majority of liver cancers are caused by chronic HBV and HCV infections, which have been estimated to be responsible for nearly 340,000 and 124,000 deaths worldwide per year respectively.⁴ The IARC Monograph identified chronic infection with HBV or HCV as Group 1 carcinogens, and that chronic HBV or HCV infections cause hepatocellular (liver) carcinoma and non-Hodgkin lymphoma (HCV only).⁷ The evidence also supports a positive association between these infections and cholangiocarcinoma (bile duct cancer) and non-Hodgkin lymphoma (HBV only).⁷

Other infections and cancer          

Other infectious agents identified in the IARC Monograph cause cancers, including gastric cancer, lymphoma, nasopharyngeal cancer, cervical cancer, anal cancer, conjunctival cancer, Kaposi sarcoma, adult T-cell leukaemia/lymphoma, cholangiocarcinoma (bile duct cancer) and urinary bladder cancer.⁷

Reducing individual risk of cancer and staying healthy

Vaccination protects against some infections, such as HPV and HBV.⁸⁷,⁸⁸ A national Australian vaccination program to protect against HPV provides free school-based vaccination to boys and girls aged 12-13, with a catch-up program during 2013-2014 for boys aged 14-15.⁸⁹ Vaccination against HBV is recommended for children as part of the National Immunisation Program.⁸⁷ More information about vaccination is available from the Immunise Australia Program.

Additional protective behaviours, such as practising safe sex and avoiding blood exposure through safe injection and blood transfusion practices, are suggested to lower risk of cancer due to infection.²,⁸²

Cancer Australia recommendations for individuals

Cancer Australia recommends vaccination to protect against HPV and hepatitis B, and other protective behaviours, such as safe sex and safe injection and blood transfusion practices, to reduce risk of hepatitis C.

Table 7: Summary of evidence for infections and cancer sites

Risk factor	Source	Evidence	Cancer site
HPV	IARC 20127	Sufficient evidence (highest IARC classification of carcinogenicity)	Cervix, vulva, vagina, penis, anus, oral cavity, oropharynx, tonsil
		Limited evidence (positive association)	Larynx
HBV and HCV	IARC 20127	Sufficient evidence (highest IARC classification of carcinogenicity)	Hepatocellular (liver) carcinoma, non-Hodgkin lymphoma (HCV only)
		Limited evidence (positive association)	Cholangiocarcinoma (bile duct cancer), non-Hodgkin lymphoma (HBV only)

See Appendix 1 for explanation of evidence.