One in every six cases of cancer worldwide can be attributed to viruses and other infectious agents, a new study from the International Agency for Research on Cancer has confirmed.
Surprised? Actually, the idea that microorganisms can cause cancer has been around for more than a century. It may help explain cancer “clusters,” in which unusual numbers of people in certain places develop cancer—liver cancer in developing countries, for example.
The infection/cancer link is good news, in a way. It means we can prevent some cancers by developing vaccines targeting organisms that cause them and/or finding other ways to prevent the infections. The vaccine for hepatitis B, for instance, prevents the kinds of chronic liver infections that often lead to liver cancer. A vaccine can now protect against strains of human papilloma virus that cause most cases of cervical cancer, as well as anal and oral cancers. Treating H. pylori, the bacterium that often causes stomach ulcers, can reduce the risk of stomach cancer.
Fortunately, most people infected with cancer-related viruses or bacteria do not develop cancer. That is, these infections are a necessary, but not sufficient, cause of cancer. Cancer is a multifactorial disorder, and other factors have to come into play. In lung cancer it’s usually tobacco smoke or radon. Diet and obesity play a role in many cancers. Aging itself is another factor. Probably most important of all is genetics. Certain genes can prevent cancer; others can give rise to it. If something—for example, a virus—somehow “turns off” the protective genes, cancer may result. Or a virus can “turn on” a gene that promotes cancer.
Vaccines that help prevent cancer will save millions of lives, especially if they can be deployed worldwide. And they raise hope for other cancers. Imagine being able to get a shot against breast, prostate or lung cancer—that’s probably a long way off, but it may happen.