"Infections with certain viruses, bacteria, and parasites are one of the biggest and preventable causes of cancer worldwide," the researchers wrote
The researchers examined a wide variety of cancer records, including a database on incidence of 27 types of cancer in 184 countries. They found that in 2008, approximately 16 percent of all cancers diagnosed could be attributed to infection. The rate of infection-related cancers was, on average, three times higher in developing countries than in richer ones, but the specifics varied widely. For example, only 3.3 percent of cancers in Australia and New Zealand could be attributed to infection, compared with a whopping 32.7 percent of all cancers in sub-Saharan Africa.
Nearly all infection-related cancers (1.9 million) were caused by one of four infectious agents: Helicobacter pylori, a bacterium of the gastrointestinal tract; the human papillomavirus (HPV); and the viruses hepatitis B and hepatitis C.
These microbes are mostly responsible for gastric, cervical and liver cancers, respectively. Approximately 50 percent of women's infection-related cancers occur in the cervix, while approximately 80 percent of men's occur in the liver, stomach and colon.
Mere infection with one of the cancer-related microbes does not guarantee the development of cancer, however.
"One thing that infection-associated cancers have in common is that a chronic infection is required," researcher Martyn Plummer said. "It takes decades for an infection to progress to cancer."
Many commentators noted that the findings give hope for dramatically reducing global cancer rates.
"Application of existing public-health methods for infection prevention, such as vaccination, safer injection practice, or antimicrobial treatments, could have a substantial effect on future burden of cancer worldwide," the researchers wrote
"The findings show the potential for preventive and therapeutic programs in less developed countries to significantly reduce the global burden of cancer and the vast disparities across regions and countries," said Harvard's Goodarz Danaei, who was not involved in the study.
"Since effective and relatively low-cost vaccines for HPV and HBV are available, increasing coverage should be a priority for health systems in high-burden countries."
A New HPV Vaccine Push?Danaei was not alone in responding to the study with a call for increased use of the controversial and potentially dangerous HPV vaccine. Referring to the HPV shot, Otis Brawley of the American Cancer Society (ACS) said, "The more people you vaccinate, male and female, the more likely you are to get a population that doesn't have the disease."
Many countries now recommend the HPV vaccine for all girls aged 11 or 12, or for unvaccinated women under the age of 27. More and more agencies, including the U.S. Centers for Disease Control and Prevention (CDC), are now recommending it for boys, as well. But a 2011 study in the Annals of Medicine warned that this pro-vaccination push may be driven by financial concerns and bad science.
In particular, the authors warned that clinical trials of Merck's HPV vaccine Gardasil used two different placebos as a way to conceal the true rates of serious side effects, and that the vaccines have never been proven effective at lowering cervical cancer rates or mortality.
"The medical profession has presented partial information to the public, namely, in a way that generates fear, thus promoting vaccine uptake," researchers Lucija Tomljenovic and Christopher Shaw of the University of British Columbia-Vancouver wrote.
"Medical and regulatory entities worldwide continue to provide inaccurate information regarding cervical cancer risk and the usefulness of HPV vaccines, thereby making informed consent regarding vaccination impossible to achieve."
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