International experts shared the complex task of tackling the exposure data, the studies of cancer in humans, 
the studies of cancer in experimental animals, and the mechanistic and other relevant data

   Results 
The evidence was reviewed critically, and overall evaluated as being limited2 among users of wireless telephones for 
glioma and acoustic neuroma, and inadequate3 to draw conclusions for other types of cancers. The evidence from the
occupational and environmental exposures mentioned above was similarly judged inadequate. The Working Group did 
not quantitate the risk; however, one study of past cell phone use (up to the year 2004), showed a 40% increased risk 
for gliomas in the highest category of heavy users (reported average: 30 minutes per day over a 10year period). 

 Conclusions
Dr Jonathan Samet (University of Southern California, USA), overall Chairman of the Working Group, indicated that 
"the evidence, while still accumulating, is strong enough to support a conclusion and the 2B classification. The conclusion means that there could be some risk, and therefore we need to keep a close watch for a link between 
cell phones and cancer risk." 

 "Given the potential consequences for public health of this classification and findings," said IARC Director 
Christopher Wild, "it is important that additional research be conducted into the longterm, heavy use of mobile phones. Pending the availability of such information, it is important to take pragmatic measures to reduce exposure such as handsfree devices or texting. " 

The Working Group considered hundreds of scientific articles; the complete list will be published in the Monograph. 
It is noteworthy to mention that several recent inpress scientific articles⁴ resulting from the Interphone study were made available to the working group shortly before it was due to convene, reflecting their acceptance for  publication at that time, and were included in the evaluation.  

A concise report summarizing the main conclusions of the IARC Working Group and the evaluations of the carcinogenic 
hazard fromradiofrequency electromagnetic fields (including the use of mobile telephones) will be published in 
The Lancet Oncology in its July 1 issue, and in a few days online. 

¹ 237 913 new cases of brain cancers (all types combined) occurred around the world in 2008 (gliomas represent 2/3 of these). 
  Source: Globocan 2008

For more information, please contact  

Dr Kurt Straif, IARC Monographs Section, at +33 472 738 511, or straif@iarc.fr; 
Dr Robert Baan, IARC Monographs Section, at +33 472 738 659, or baan@iarc.fr; or 
Nicolas Gaudin, IARC Communications Group, at com@iarc.fr (+33 472 738 478) 

Link to the audio file posted shortly after the briefing:
https://terrance.who.int/mediacentre/audio/press_briefings/

 About IARC 

The International Agency for Research on Cancer (IARC) is part of the World Health Organization. Its mission is to 
coordinate and conduct research on the causes of human cancer, the mechanisms of carcinogenesis, and to develop 
scientific strategies for cancer control. The Agency is involved in both epidemiological and laboratory research and 
disseminates scientific information through publicaions, meetings, courses, and fellowships. 

Nicolas Gaudin, Ph.D. 
Head, IARC Communications
International Agency for Research on Cancer
World Health Organization 
150, cours AlbertThomas 
69008 Lyon  France 
Email com@iarc.fr
https://www.iarc.fr/   

ABOUT THE IARC MONOGRAPHS

What are the IARC Monographs? 

The IARC Monographs identify environmental factors that can increase the risk of human cancer. These include 
chemicals, complex mixtures, occupational exposures, physical and biological agents, and lifestyle factors. National 
health agencies use this information as scientific support for their actions to prevent exposure to potential carcinoens. 
Interdisciplinary working groups of expert scientists review the published studies and evaluate the weight of the 
evidence tha an agent can increase the risk of cancer. The principles, procedures, and scientific criteria that guide the 
evaluations are described in the Preamble to the IARC Monographs. 

Since 1971, more than 900 agents have been evaluated, of which approximately 400 have been identified as 
carcinogenic or potentially carcinogenic to humans. 

Definitions

Group 1: The agent is carcinogenic to humans. 
This category is used when there is sufficient evidence of carcinogenicity in humans. Exceptionally, an agent may be
 placed in this category when evidence of carcinogenicity in humans is less than sufficient but there is sufficent 
evidence of carcinogenicity in experimental animals and strong evidence in exposed humans that the agent acts 
through a relvant mechanism of carcinogenicity. 

Group 2. 
This category includes agents for which, at one extreme, the degree of evidence of carcinogenicity in humans is 
almost sufficient, as well as those for which, at the other extreme, there are no human data but for which there is 
evidence of carcinogenicity in experimental animals. Agents are assigned to either Group 2A (probably carcinogenic 
to humans) or Group 2B (possibly carcinogenic to humans) on the basis of epidemiological and experimental evidence 
of carcinogenicity and mechanistic and other relevant data. The terms probably carcinogenic and possibly carcinogenic
have no quantitative significance and are used simply as descriptorsof different levels of evidence of human 
carcinogenicity, with probably carcinogenic signifying a higher level of evidence than possibly carcinogenic. 

Group 2A: The agent is probably carcinogenic to humans. 
This category is used when there is limited evidence of carcinogenicity in humans and sufficient evidence of 
carcinogenicity inexperimental animals. In some cases, an agent may be classified in this category when there 
is inadequate evidence of carcinogenicity in humans and sufficient evidnce of carcinogenicity in experimental 
animals and strong evidence that the carcinogenesis is mediated by a mechanism that alsooperates in humans. 
Exceptionally, an agent may be classified in this category solely on the basis of limited evidence of carcinogenicity 
in humans. An agent may be assigned to this category if it clearly belongs, based on mechanistic considerations, to a 
class of agents for which one or more members have been classified in Group 1 or Group 2A.

Group 2B: The agent is possibly carcinogenic to humans. 
This category is used for agents for which there is limited evidence of carcinogenicity in humans and less than 
sufficient evidnce of carcinogenicity in experimental animals. It may also be used when there is inadequate evidence 
of carcinogenicity in humans but there is sufficient evidence of carcinoenicity in experimental animals. In some 
instances, an agent for which there is inadequate evidence of carcinogenicity in humans and less than sufficient 
evidence of carcinogenicty in experimental animals together with supporting evidence from mechanistic and other 
relevant data may be placed in this grop. An agent may be classified in this category solely on the basis of strong 
evidence from mechanistic and other relevant data. 

Group 3: The agent is not classifiable as to its carcinogenicity to humans. 
This category is used most commonly for agents for which the evidence of carcinogenicity is inadequate in humans 
and inadequateor limited in experimental animals. 
Exceptionally, agents for which the evidence of carcinogenicity is inadequate in humans but sufficient in experimental 
animals may be placed n this category when there is strong evidence that the mechanism of carcinogenicity in experimental animals does not operate in humans. 
Agents that do not fall into any other group are also placed in this category.
An evaluation in Group 3 is not a determination of noncarcinogenicity or overall safety. It often means that further  research is needed, especially when exposures are widespread or the cancer data are consistent with differing interpretations. 

Group 4: The agent is probably not carcinogenic to humans. 
This category is used for agents for which there is evidence suggesting lack of carcinogenicity in humans and in 
experimental aimals. In some instances, agents for which there is inadequate evidence of carcinogenicity in humans 
but evidence suggesting lack of carcinogenicity in xperimental animals, consistently and strongly supported by a 
broad range of mechanistic and other relevant data, may be classified in this group. 

Definitions of evidence, as used in IARC Monographs for studies in humans
The evidence relevant to carcinogenicity from studies in humans is classified into one of the following categories:  

Sufficient evidence of carcinogenicity: The Working Group considers that a causal relationship has been established between exposure to the agent and  human cancer. That is, a positive relationship has been observed between the exposure and cancer in studies in which chance, bias and confounding could be ruled out with reasonable confidence.
A statement that there is sufficient evidence is followed by a separate sentence that identifies the target organ(s) or tissue(s) where an increased risk of cancer was observed in humans. Identification of a specific target organ or tissue does not preclude the possibility that the agent may cause cancer at othersites. 

Limited evidence of carcinogenicity: A positive association has been observed between exposure to the agent and cancer  for which a causal interpretation is  consideed by the Working Group to be credible, but chance, bias or confounding could not be ruled out with reasonable confidence. 

Inadequate evidence of carcinogenicity: The available studies are of insufficient quality, consistency or statistical power to permit a conclusion regarding the presence or absence of a causal association between expoure and cancer, or no data on cancer in humans are available. 

Evidence suggesting lack of carcinogenicity: There are several adequate studies covering the full range of levels of exposure that humans are known to encounter, which are mutually consistent in not showing a positive association between exposure to the agent and any studied cancer at an observed level of exposure. The results from these studies alone or combined should have narrow confidence intervals with an upper limit close to the nullvalue (e.g. a relative risk of 1.0). Bias and confounding should be ruled out with reasonable confidence, and the studies should have an adequate length of follow up. A conclusion of evidence suggesting lack of carcinogenicity is inevitably limited to the cancer sites, conditions and levels of exposure, and length of observation covered by the available studies. In addition, the possibility of a very small risk at the levels of exposure studied can never be excluded. 

In some instances, the above categories may be used to classify the degree of evidence related to carcinogenicity in specific organs or tissues.