Bacteria, viruses and parasites cause around two million cases of cancer in the world each year, experts believe. Of the 7.5 million global deaths from cancer that occurred in 2008, an estimated 1.5 million may have been due to potentially preventable or treatable infections.
Scientists carried out a statistical analysis of cancer incidence to calculate that around 16% of all cancers diagnosed in 2008 were infection-related. The proportion of cancers linked to infection was three times higher in developing than in developed countries.
Key cancer-causing infectious agents include human papillomavirus (HPV), the gastric bug Helicobacter pylori and the hepatitis B (HBV) and C viruses. These four were together believed to be responsible for 1.9 million cases of cancer, mostly gastric, liver and cervical cancers.
Cervical cancer accounted for around half of infection-related women's cancers. In men, more than 80% of infection-related cancers affected the liver, stomach and colon.