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Thursday, May 10, 2012

Contagious cancers

Why are so many people still getting cancer? The unfortunate answer may be that they caught it from someone else. Let me back track and say that cancer itself is not contagious. However, many cancers are originally caused by infectious agents like viruses.  How many? Catherine de Martel and her colleagues from the International Agency for Research on Cancer, France, estimate that around 16% of all cancers worldwide began as infections.

Ninety-five percent of those two million new cancer cases per year are attributable to just four types of viruses: Helicobacter pylori, hepatitis B and C viruses, and human papillomaviruses. This is actually good news, because we have vaccines against many of these agents. In fact, vaccination against viral cancers is probably reflected in the data, since more affluent countries have a far lower rate of these kinds of cancers. While only about 7% of cancers in developed countries were caused by infection, 33% of cases in sub-Saharan Africa fell into that category.

Cancer is considered to be non-communicable, and that’s still largely true. Not only are the majority of cancers not caused by infectious agents, but those that are tend to be caused by viruses that are not that easy to catch. These are not infections you’d get from hugging someone. Nevertheless, it’s important to recognize the role that viruses play in causing cancer, and the role that vaccination may play in preventing cancer.

As we learn more about both cancer and virology, it may be that more cancers with previously unknown provenance become attributable to viral infection. On the other hand, Ed Yong, who writes the Not Exactly Rocket Science blog for Discovery Magazine, points out that the proportion of cancers that result from infections has not changed for more than a decade.