Backgrounder: Cellphones And Cancer : Shots - Health News Researchers have yet to find a clear link between cellphones and cancer. Here's a summary of what they know so far.

Backgrounder: Cellphones And Cancer

After reviewing some of the latest scientific studies, the World Health Organization has decided to add cellphones to its lengthy list of things that could possibly cause cancer. With a few billion people worldwide now using the devices, scientists at the WHO say there are enough hints in the data that cellphones should be listed as "possible carcinogens" — with the emphasis on "possible."

Researchers have yet to find a clear link between cellphones and cancer. Here's what they know so far:

  • The types of brain cancer cellphones are suspected to cause — glioma and meningioma -- are still rare, affecting only 6 to 7 per 100,000 Americans. And despite a dramatic rise in cellphone use, two major studies show the rate of these brain cancers between 1992 and the mid-2000s has essentially remained unchanged. You would expect to see a rise in that brain cancer as cellphone usage grows.
  • One 2010 study found a small increase in tumors in women — from 2.5 cases per 100,000 people to 2.6 cases per 100,000. Those cases occurred in the brain's frontal lobe. But researchers say it's unlikely radiation from a cellphone would bypass tissue closer to the ear and affect only the frontal lobe.
  • Last year, the largest study conducted to date found scant evidence to support a link. "Overall, no increase in risk of glioma or meningioma was observed with use of mobile phones," the authors for the WHO study concluded.
  • That study and others have raised questions about a phenomenon called "recall bias." WHO researchers asked people to remember how often they used their cellphones more than a decade ago, and the men and women with brain cancer recalled a disproportionately high use of cellphones, while others recalled disproportionately low exposure. In other words, people with cancer or an illness sometimes distort memories in search of a cause of their illness.
  • In another study published earlier this year in the Journal of the American Medical Association, brain researchers found that waves from a cellphone can affect the brain's metabolism. But researchers say there's no evidence that an increase in brain metabolism is harmful or is linked to cancer.
  • Two major trials are currently under way in the U.S. and Europe. Oncologist and author Siddhartha Mukherjee tells NPR's Talk of the Nation those studies eventually "will settle the issue once and for all." But, thus far, he says, "I would say the evidence remains pretty negative."