One in every six cancer deaths worldwide is caused by preventable infections, a total of 1.5 million deaths yearly that could be halted by widespread vaccination programs, researchers reported Wednesday. Since 1990, that number has grown by about half a million, suggesting that vaccination programs are losing ground in the battle rather than gaining it. The vast majority of the cases are caused by three viruses and a bacterium, which are the leading causes of gastric, liver and cervical cancers. Cervical cancers account for about half of the infection-related cancers in women, while liver and gastric cancers account for about 80% of those in men.

The causes of many cancers are largely unknown, but genetics and poor luck play big roles. The World Health Organization estimated in 2004 that nine lifestyle and environmental factors -- smoking being a particularly large one -- account for as many as 35% of the 12.7 million cancers that occur each year, about twice the proportion now linked to infections.

Cervical cancers are caused primarily by the human papilloma virus (HPV), as are anal and penile tumors. Stomach cancers are caused by the bacterium Helicobacter pylori. The hepatitis B and hepatitis C viruses cause liver cancer. All such infections are readily preventable by vaccination. Other less common agents include the Epstein-Barr virus, which causes nasopharynx tumors and Hodgkin’s lymphoma; human herpes virus type 8, which causes Kaposi’s sarcoma, usually in conjunction with HIV; and the parasite Schistosoma haematobium, which causes bladder cancer.

A team headed by Dr. Catherine de Martel and Dr. Martyn Plummer of the International Agency for Cancer Research in Lyon, France, used data compiled by the agency’s GLOBOCAN program to estimate the cancer incidence in various regions of the world, then used actual data of various cancers as well as estimates to predict the total attributable to infectious agents. They reported in the journal Lancet that the worldwide average of cancers caused by infectious agents was 16.5%, with about three times more (22.9%) occurring in developing countries than in developed countries (7.4%). Rates varied widely between regions, ranging from a low of 3.3% in Australia and New Zealand to a high of 32.7% in sub-Saharan Africa. About 4% of cancers were caused by infectious agents in North America and 7% in Europe.


In an editorial accompanying the report, Dr. Goodarz Danaei of the Harvard School of Public Health in Boston noted that vaccines for HPV and hepatitis B are available at a “relatively low cost” and “increasing coverage [with them] should be a priority for health systems in high-burden countries.”

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