Almost 1 in 6 cases of cancer is caused by an infectious agent according to a new study published online in The Lancet this month. The study also found that the burden of infection-related cancers was higher in the developing world, in women, and in younger individuals.
Researchers from the International Agency for Research on Cancer (IARC), Lyon, France, analysed country specific cancer incidence data, to determine the proportion of cancers in each country that were attributable to infections. The researchers found significant disparities in rates of infection-related cancers between developing and developed countries. In total, around 2 million of the 12.7 million cancers worldwide in 2008, or 16.1%, were estimated to be the result of infection. In developing countries the proportion was 22.9% compared to just 7.4% in developed countries. New Zealand and Australia had the lowest proportions with 3.3%. Rates in North America and Europe were 4% and 7% respectively. The proportion was highest in sub-Saharan Africa with 32.7% of all cancers due to infection. North Africa, West Asia, and South East Asia also had relatively high proportions.
Infection-related cancers were slightly more common in women than men (1.1 million vs 0.9 million). Almost half of the cancers in women were cervical cancers while more than three quarters of male infection-related cancers were of the liver and stomach.
The burden of infection-related cancers was higher in the young. Only 21% of all cancers are diagnosed in individuals aged under 50 however 30% of all infection related cancers occur in this age group.
The researchers found that four infectious agents accounted for the vast majority of infection related cancers – around 1.9 million of the 2 million cases. These were hepatitis B & C, human papillomaviruses (HPV), and Helicobacter pylori.
Helicobacter pylori infection increases stomach cancer risk and is responsible for an estimated 65% of stomach cancers and 5.5% of total cancers.
The vast majority (>80%) of all cervical cancers are the result of infection with one of the many variants of HPV. HPVs are also a significant risk factor for oral and anal cancers. Around 5.2% of total cancers are the result of HPV infection.
Infection with either Hepatitis B or C increases the risk of developing liver cancer, with around 75% of all liver cancers, and 4.9% of total cancers thought to be the result of hepatitis infection.
Other infections known to be carcinogenic include Epstein-Barr virus (EBV), Human T-lymphotropic virus (HTLV), Kaposi’s sarcoma-associated herpesvirus (KSHV), and human immunodeficiency virus (HIV).
While infections may cause 16% of all cancers, lifestyle factors cause many more – an estimated 25%. These include heavy alcohol consumption, smoking, a sedentary lifestyle, poor diet (high red meat consumption and low fiber, fruit, and vegetable intake), oral contraceptive use, and hormone replacement therapy.
The graph below shows a breakdown of cancer incidence by site for the developed and developing world. Cancers that are related to lifestyle such as breast, colorectal, prostate, and lung cancer, are much more common in developed countries while cancers primarily caused by infection, such as cervical, stomach, and liver cancer are more common in developing countries.
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