It seems official – but its conclusions are no different from earlier ones. On May 27, a major rat study by the US National Toxicology Program (NTP) claimed to link cellphone radiation to cancer. The NTP found low incidences of tumours in the brains and hearts of male rats, but not in female rats exposed to cellphone radiation. The $25-million study is the largest and the most complex ever conducted by the NTP, yet a closer review reveals that it raises more questions and remains inconclusive.
Specialists have appreciated the uniqueness of the study but roundly criticised it for its glaring pitfalls. The researchers who conducted the study could not explain some findings. For instance, exposed rats lived longer than the controls (i.e., which weren’t exposed; could this mean that cell phone radiation is beneficial?). In addition, rats in the control groups did not suffer from any cancer. Note: The NTP continues its study on mice, with the complete results expected by the end of 2017.
We must not ignore the research because studies like the NTP’s are few. The critical appraisal is not to belittle its significance. The cancer risk, if any, from cellphone-use continues to be low. After all, there has been no noticeable increase in brain tumours in various countries for the past several decades. Unfortunately, less accurate and provocative media coverage of this study may excite raw emotions even as the perceived harm in this instance is more that the actual harm. Possible cancer induction by cellphone radiation concerns people. Anecdotal evidence and highly publicised litigations filed by persons claiming that cellphone radiation injured them fan the fire.
The study’s rationale
These fears led to epidemiological studies trying to identify the role of cellphone radiation as a carcinogen. Details of most of the important studies are available in a factsheet published by the National Cancer Institute.
In 2013, after reviewing the studies published till then, the International Agency for Research on Cancer (IARC) classified radio-frequency radiation (RFR) as class 2B, a possible human carcinogen based on:
- “limited evidence” of an association between exposure to RFR from heavy wireless-phone-use and glioma and acoustic neuroma in human epidemiology studies, and
- “limited evidence” for the carcinogenicity of RFR in experimental animals.
Some try to dismiss the impact of the IARC classification saying that the class-2B carcinogens include coffee and pickles.
Since various studies and their analyses were weak, the US Food and Drug Administration nominated the NTP to undertake its study. In it, researchers exposed rats and mice in specially designed reverberation chambers to electromagnetic radiation of frequencies and modulations presently used in cellular communications in the United States. They exposed them for nine hours daily – 10 minutes at a time followed by a 10-minute break – from before birth until they turned two years old. They chose four dose levels: zero (for the control group), and 1.5 W, 3 W and 6 W per kg of tissue mass.
Some 2-3% of the exposed male rats developed gliomas, a brain cancer, compared with none in a control group. About 5-7% of the male rats exposed to the highest level of radiation developed schwannomas (tumours that occur in cells lining the nerves) in their hearts, compared with none in the control group. The authors then concluded that the brain and heart tumours were “likely caused’’ by the radiation.
Dr. Michael S. Lauer, of the office of extramural research at a National Institute of Health, was one of the outside reviewers chosen by the NTP. He listed many shortcomings of the project. “I suspect that this experiment is substantially underpowered and that the few positive results found reflect false positive findings,” he asserted. “The higher survival with RFR, along with the prior epidemiological literature, leaves me even more skeptical of the authors’ claims.”
Kenneth R. Foster, a professor of bioengineering at the University of Pennsylvania, who was not associated with the study, conceded that it did receive a lot of attention. Quoting one of the reviewers, he pointed out that the historical incidence of glioma in rats is 1.7% (about what was found in the exposed rats). The study found no gliomas in the control rats but the incidence was not zero. The reviewer argued that if you assume, plausibly, one glioma in the controls, the statistical significance vanishes or at least becomes much weaker. “In other words, fragile results, the usual problem with ‘small n’ studies,” Foster clarified. He was referring to the inherent frailty of studies involving a small number of effects.
More radiation than at play
Additionally, he pointed out that the exposure levels (1.5, 3 and 6 W/kg) were thermally significant. “At 6 W/kg, rats in previous studies experienced work stoppage – shifting from assigned tasks to thermo-regulatory behavior such as spreading saliva on the tail, reflecting excessive heating to the animals [in human terms, they felt the need to cool off, which rats do by spreading saliva on their tails]. Such exposure levels would trigger all sorts of thermally induced changes in the animals,” he explained.
According to Foster, the paper is bound to attract the attention of health agencies, which will review the results in great detail before forming opinions. As for his: “The results strike me as weak, only male rats showed gliomas (not females). The exposure levels were thermally significant to the animals and at the higher two exposure levels, the animals may have been thermally stressed. [There is] no clear dose-response relation, no big changes in incidence over a four-fold range of exposure.”
He further added, in an email to this correspondent, “The authors mention (I think) that the exposed animals lived longer than the controls. Since cancers tend to appear late in life, this aspect of the result needs to be explored, and some data is needed for incidence of these kinds of cancers in the strain of rats that were used. In short, the results are suggestive but not definitive. Note that the exposures were far above anything that would be permitted by RF safety limits.”
Will the result lead to a reclassification of cell phone radiation by the WHO or the IARC? According to Foster, “It may lead to more ‘precautionary’ advice (using hands free kits), and possibly IARC will upgrade its classification of RF from 2B (possible) to 2A (probable) – but I am not sure about that.”
“Of course, the activists, who seem to suffer from extreme confirmation bias, will pick up on this study and say that it confirms their worst fears,” Foster added. “Given the lack of evidence for an increased incidence of brain tumours in the population in recent decades, I do not expect health agencies to react very strongly to these findings, but they certainly will examine them carefully.”
In a detailed review, R. Mark Simpson, affiliated with the laboratory of cancer biology and genetics, the National Institutes of Health, prepared a working list of limitations that could potentially impact how the NTP study is interpreted. Following up, Dr. Vijayalaxmi, of the department of radiology at the University of Texas Health Science Centre, said in an email, “I am not sure that one single NTP data (only male rats showing increased tumours and NOT female rats) would [prompt] IARC to reclassify 2B status of cellphones when there are [more than] 40 peer-reviewed scientific publications already in the literature contradicting these observations.” She was not associated with the NTP study. She is an established researcher in the field and was a member of the WHO/IARC working group, which recommended that RF electromagnetic fields be classified as class-2B carcinogens.
In a press release from the American Cancer Society (ACS), Dr. Otis W. Brawley, the chief medical officer, referred to the NTP study as “good science” even as the statement highlighted some of the study’s limitations. “While this study adds significantly to the evidence that cellphone signals could potentially impact human health, it does not actually tell us how certain scenarios of cellphone use change our long-term risks of getting cancer. For example, the animal studies were performed at very high signal strengths, near but below levels that would cause animal tissue to heat up,” Dr. Brawley himself cautioned. “Additional research will be needed to translate effects at these high doses to what might be expected at the much lower doses received by typical or even high-end cellphone users. Also, cell phone technology continues to evolve, and with each new generation, transmission strengths have declined and with it radio frequency exposures.
Most media outlets reacted appropriately (while there were some exceptions). The headline of an article in the San Diego Union-Tribune on May 27 went “Reasons for skepticism about cell phone/cancer study”. The author, Bradley J. Fikes, outlines nine reasons to suspect the study as well as notes that Marty Cooper, widely considered to be the father of the cellphone, does not think much of the results. Fikes quotes Cooper as saying, “I have been studying the possibility of effects of [RF] radiation on people for over sixty years. No responsible scientist would make a statement like the one in this article. To the nine valid comments you made, add that the correlation of rat cancer to people cancer has not been established,” Cooper added.
K.S. Parthasarathy is a former Secretary, Atomic Energy Regulatory Board. He can be reached at firstname.lastname@example.org.