Do cell phones cause cancer? It’s a highly pertinent question considering that 5 billion people worldwide are expected to use mobile phones by 2017.1 The general causation risk scores on CoMeta™ for cell phones (“Radiofrequency Fields-Wireless Telephones”) indicate that there is not a consensus in the scientific literature that cell phone exposure causes cancer.
Although a number of studies report positive correlations between cell phone use and cancer, even more studies report no such association. Moreover, three additional factors cast doubt on whether cell phone exposure causes cancer: the overall incidence of brain cancer is decreasing, there is no known cellular mechanism by which cell phones can cause cancer, and cell phones have been in use long enough for the estimated latency period for most forms of brain cancer to have passed. Yet there continues to be concern about this potential risk, and fears remain heightened with the release of preliminary results from an unprecedented $25 million animal study by the U.S. National Toxicology Program (NTP) in May 2016.2
The NTP began examining the link between cell phones and cancer in 2012. The study, the largest ever conducted by the NTP, exposed mice and rats to nine hours of full body radiofrequency (RF) radiation at two different frequencies that mimic cell phone exposure. The preliminary results only cover two of the test configurations: rats exposed to the lower frequency of RF radiation, using both signal modulations, and at different intensities as measured by specific absorption rate (SAR). SAR is a biological measure of exposure based upon the amount of radiofrequency energy that is absorbed into the organism or tissues. The Federal Communications Commission limit for human exposure from cell phones is set at a SAR of 1.6 W/kg and requires all devices approved for sale to separately measure the SAR for the head and the full body. The SARs in the NTP study ranged from 0-6 W/kg and are whole-body radiation.
The study’s preliminary results surprised many experts: Male rats exposed to radiofrequency fields had a significantly increased incidence of tumors in the brain and heart relative to unexposed controls.
Upon the NTP’s release of the preliminary results, the press characterized the findings as “explosive.”3 But are they? The NTP’s results are provocative, but they also raise a number of important questions. Reviewers chosen by the NTP to comment on the study point out three key issues that confound the interpretation of the study’s findings. First, the rate of tumors among the rats in the control group is low, suggesting that the control group is not representative of the rat population in general. Recalculating the results using the average historical cancer rate for the control group would eliminate the estimated treatment effect. Next, despite the increased cancer rate among the exposed population, the average lifespan of the exposed population was longer than that of the control group. The control group survival rate of 28% is toward the lower range of survival rates in NTP studies in general; the average control group survival rate for rats in NTP studies is closer to 50%. If brain cancer is more likely to develop later in life, then the low survival rate impacts the researchers’ ability to determine the true incidence of cancer among the controls. Finally, only male rats were at a significantly greater risk of cancer, and there is no understood mechanism as to why this risk would be sex-specific. Other experts also question whether results generated from whole body exposure and this specific range of SARs are relevant to understanding the cancer risk from human exposure to the head at lower SARs.
The general causation risk score puts as much weight on NTP studies as it does on studies published in the best scientific journals (e.g., Science, New England Journal of Medicine). Even so, a single animal study will move the needle on scientific consensus only so much in a literature saturated with conflicting human evidence. More positive animal and human studies will need to be published before we observe a significant shift in the general causation risk score for the cell phone-cancer hypothesis. This is always possible, and CoMeta stands ready to incorporate this evidence as it emerges, but the concerns about the NTP study voiced by experts in the field suggest that replication of these surprising results are perhaps less likely than one would normally expect.
Sally Embrey is a bioscience knowledge engineer at Praedicat.
You can reach Sally by email at email@example.com