IARC uses five categories to classify the carcinogenic risk of thousands of agents, mixtures, and exposures:
- Group 1: carcinogenic to humans.
- Group 2A: probably carcinogenic to humans.
- Group 2B: possibly carcinogenic to humans.
- Group 3: not classifiable as to carcinogenicity in humans.
- Group 4: probably not carcinogenic to humans. (Wikipedia, http://bit.ly/1nDkrgE)
By the way, I have no conflicts of interest; Dr. Muhkerjee's recent lecture was co-sponsored by the cellphone operators association of India.
Photo caption: Pulitzer award winning India-born oncologist Dr Siddhartha Mukherjee addresses a press conference in the capital on Monday.
Summary: Calls for revision of World Health Organization’s list of carcinogens, says not enough data to establish the link.
Dr Mukherjee, author of the Pulitzer winning book The Emperor of All Maladies: A Biography of Cancer that was published in 2010, is currently in India to accept the Padmashree award. He is an assistant professor of medicine at Columbia University and a staff physician at Columbia University Medical Center in New York City.
In a recent article in The New York Times he had argued that the drastic increase in cellphone usage does not mirror incidence of brain cancer, neither is the radiation emitted by cellphones of the nature that can directly damage DNA. He also termed as “loose” WHO’s definition of “possible carcinogens”, some of which “defies logic” in their proclivity to be more conservative.
However, he says, “The last word has not been said on the matter of cellphone radiation and cancer. The interphone trials (that sought to examine the link) have a serious recall bias — people did not always correctly recall the extent of their cellphone usage. There is a need to examine how radiation of that wavelength can be carcinogenic. I would ask WHO to downgrade cellphone radiation in the list of carcinogens, which includes coffee. But I am willing to revise this assessment if there is additional data available.”
But he says there is not enough data to make a similar claim about radiation emitted by cellphone towers ...
April 21, 2011
Siddhartha Mukherjee, M.D., Ph.D.
Herbert Irving Cancer Research Center (Audubon III )
Room 603 1130 St. Nicholas Avenue
New York, NY 10032
Dear Professor Mukherjee:
First, I would like to congratulate you on your Pulitzer Prize. I look forward to reading your book.
I am writing you about your recent New York Times magazine article and NPR interview about cell phone radiation and brain tumor risk. Although I agree that epidemiologic research does not yield conclusive evidence, my colleagues and I have carefully read and analysed this research and conclude that the evidence is highly suggestive of increased brain tumor risk due to prolonged cell phone use.
My colleagues and I published a meta-analysis of 23 case-control studies (Myung, SK, Ju W, McDonnell DD, Lee YJ, Kazinets G, Cheng C-T, Moskowitz JM. Mobile phone use and risk of tumors: A meta-analysis. Journal of Clinical Oncology. 2009. 27(33):5565-5572). Although overall we found no evidence of increased tumor risk (including brain, eye, facial nerve, salivary gland, NHL), in our opinion it is a mistake to simply look at the “weight of the evidence” as many scientific committees and government health agencies have done, because not all of the evidence warrants equal weight. In our meta-analysis, cell phone use was associated with significantly increased tumor risk in the high quality or non-industry-funded studies, and significantly associated with decreased tumor risk in the low quality or industry-funded studies. The latter findings were most likely attributable to bias. Moreover, we found that 10 or more years of cell phone use was associated with significantly increased brain tumor risk. Another recent review obtained similar results (Khurana VG, Teo C, Kundi M, Hardell L, Carlberg M. Cell phones and brain tumors: a review including the long-term epidemiologic data. Surgical Neurology. 2009. 72(3):205-14.)
Since these two review papers were published, pooled results from the Interphone study were published from data collected in 13 nations between 2000 and 2004 (Interphone Study Group. Brain tumour risk in relation to mobile telephone use: Results of the INTERPHONE international case-control study. International Journal of Epidemiology. 2010. 39(3):675-694). Like many other epidemiologic studies, most participants in Interphone hardly used cell phones. In fact, the typical user had fewer than 100 hours of lifetime use. Furthermore, as you know brain tumors can take decades to develop so it’s unrealistic to expect to see increased tumor risk in the short term. The typical user in the Interphone study had their phones for about five years.
We agree that the quality of the epidemiologic research has been problematic, and that one cannot draw causal inferences from case-control studies. The Interphone study had numerous problems which have been discussed in the literature (Morgan, LL. Estimating the risk of brain tumors from cellphone use: Published case-control studies. Pathophysiology. 2009. 16(2-3):137-147). However, most of these biases work against finding increased tumor risk.
The final analyses reported in the second appendix to the Interphone study corrected for what was likely the most important study bias—participation bias. These analyses found a “dose-response relationship”—increased glioma risk with increasing number of years of cell phone use. Among those who used cell phones 10 or more years, Interphone found more than a doubling of glioma risk compared to cell phone users of less than 2 years. These results were similar to those found in a study conducted by Lennart Hardell and colleagues in Sweden. (In these analyses, the risk estimate for the highest decile of use group increased from 1.40 reported in Table 2 to 1.80.)
Three Interphone study investigators including the lead investigator, Elisabeth Cardis, along with Siegal Sadetzki and Bruce Armstrong, have recently called for precautionary health warnings. About a dozen nations have issued warnings to limit children’s cell phone use or to keep cell phones a safe distance from the body, especially the head and genitals. Typical recommendations include use of a wired headset, speakerphone or text and not use phones in locations with weak signals or in moving vehicles.
In addition to the epidemiologic evidence for tumor risk, there is considerable evidence from animal and cellular studies of biologic reactivity to cell phone radiation. Here, too, the evidence is inconsistent, but according to a review by Henry Lai, the research conducted independent of industry funding was far more likely to find harmful effects than industry-funded studies.
The U.S. government needs to cultivate and fund a scientific community that operates independent of industry for us to develop an unbiased, scientific knowledge base that can be used to develop policies that minimize population health risks from the adoption of EMF technologies. A $1 per year fee on cell phones would generate $300 million annually for this work.
Although brain tumors are rare and the research on cell phone radiation is not yet conclusive, with more than 300 million cell phones in use in the U.S. we believe it is imprudent from a public health standpoint to wait before issuing precautionary health recommendations. At a minimum, precautionary principle actions are immediately warranted.
Please feel free to call me if you would like to discuss these issues.