Tuesday, August 11, 2026

NTP Cellphone Carcinogenicity Study: Followup Studies

Flawed "Validation" Studies Do Not Negate Established Evidence 
That Cell Phone Radiation Causes Cancer in Rats

Summary: A new paper published in Environmental Health finds that the Japanese and Korean cell phone radiation cancer studies do not prove cell phone safety, as they were underpowered and used too few exposure doses to legitimately challenge the U.S. National Toxicology Program’s landmark findings of increased cancer from long-term cell phone radiation exposure. Long-overdue policy changes to reduce public exposure are urgently needed.

A new peer reviewed paper published in the journal Environmental Health states that two industry-linked “validation” studies from Japan and Korea published in 2026, designed to verify the U.S. National Toxicology Program’s (NTP) finding that cell phone radiofrequency (RF) radiation causes cancer in rats, were so underpowered and narrowly designed such that they could never have confirmed or refuted the original results, regardless of the outcome. The authors state that these “validation” studies should not comfort the public when it comes to the safety of cell phones and other wireless devices.

The paper “Conflicting views in experimental carcinogenesis: A commentary on design and methodological deficiencies in the follow-up validation studies on radiofrequency radiation,” authored by Ronald L. Melnick (formerly of the National Institute of Environmental Health Sciences), Joel M. Moskowitz (University of California, Berkeley), and Paul Héroux (McGill University) on behalf of the International Commission on the Biological Effects of Electromagnetic Fields (ICBE-EMF), examines the design and interpretation of the Japan and Korea studies against long-standing scientific and regulatory standards for animal carcinogenicity testing.

Background

In 2011, the World Health Organization’s International Agency for Research on Cancer (IARC) classified RF radiation as “possibly carcinogenic to humans,” based largely on results from human epidemiological studies. In 2018, the National Toxicology Program, which is part of the U.S. Department of Health and Human Services, issued the final report of their $30 million animal studies concluding there is “clear evidence” that male rats exposed to cell phone (RF) radiation for two years developed malignant heart schwannomas, a rare tumor, along with “some evidence” of brain gliomas and adrenal tumors. The NTP study was designed to provide greater sensitivity than international guidelines for rigorous cancer-testing.

A study conducted by the Ramazzini Institute in 2018 reported increased tumors similar to those observed in the NTP. These new animal cancer findings, along with additional human studies, prompted the WHO/IARC advisory group to repeatedly recommend a new evaluation of the scientific evidence on the carcinogenicity of wireless radiation. Many scientists with expertise in environmental carcinogenicity then published their conclusion that the current evidence is now consistent with IARC criteria for the classification of wireless RF radiation as a “probable human carcinogen”  (IARC Group 2A), or even  “carcinogenic to humans” (Group 1).

However, after the NTP study was released, new animal studies were launched in Japan and Korea, under an “International Validation Project,” aiming to test whether the NTP’s findings were reproducible. Their results, separately published in 2026, concluded that long-term RF radiation exposure did not produce reproducible carcinogenic or genotoxic effects.

However, according to the new paper, the Japanese and Korean animal studies did not replicate the NTP study and had several deficiencies, including:

  • Severely Reduced Statistical Power: The follow-up studies used only 70 animals per group, compared to 90 per group in the NTP study. Power calculations indicate that detecting a significant response for rare tumors at the lower exposure level used in those studies would require many more animals per group.
  • Omission of High-Dose Groups: The follow-up studies tested only a single exposure level (4 W/kg) and dropped the NTP’s highest exposure level (6 W/kg), where significant carcinogenic effects were most statistically pronounced.
  • Violation of FDA and the Organization for Economic Co-operation and Development Guidelines: Testing guidelines by these groups require at least three different doses plus a control group to conduct a critical dose-response trend analysis. Single-dose studies eliminate the ability to detect dose-dependent trends.
  • Overlooked Signals of Harm: Despite being underpowered, the Korean study actually observed a 3% incidence rate of heart schwannomas in exposed rats (versus 0% in controls), matching the tumor rate observed at 3 W/kg in the NTP study, yet the researchers surprisingly dismissed the finding.
  • Prominent Role of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and Industry-Friendly Advisors: The project’s principal investigator was an ICNIRP member, and the advisory committee overseeing the research was heavily composed of current and former ICNIRP members, several of whom have served as industry consultants. The Japan/Korea studies were aimed at protecting ICNIRP’s current cell phone radiation safety limits rather than at documenting radiation risks.

The authors of the new analysis conclude that the Japan and Korea studies’ conclusion of “no reproducible carcinogenic potential” of cell phone radiation is simply not supported by the studies’ design and, in the case of the Korean study, is undercut by its own data. Therefore, the Japan and Korea studies do not alter the National Toxicology Program’s finding of “clear evidence” of cancer.

In a paper published earlier this year, Melnick and Moskowitz concluded that, based on the NTP cancer findings, current FCC and ICNIRP exposure limits would need to be at least 200 times lower to protect against cancer risk from 8 hours of daily exposure. The International Commission on the Biological Effects of Electromagnetic Fields is calling on governments to implement policies that reduce public exposure and inform cell phone users on how to minimize their risk.

Ronald L. Melnick, PhD, lead author and retired toxicologist at the National Institute of Environmental Health Sciences, who led the design of the original NTP radiofrequency radiation studies:

“The Japan and Korea studies cannot be used as proof of safety. To properly verify a study that found clear evidence of rare tumors like heart schwannomas, follow-up research must be designed with equal or greater sensitivity. By dropping the highest exposure level, testing only a single dose, and using fewer animals, these follow-up underpowered studies failed to meet basic FDA and OECD testing guidelines and were systematically biased toward finding no significant effect. These studies appear to be engineered to come back negative, no matter what the true biology is.

In short, the Japan and Korea studies cannot be used to invalidate the National Toxicology Program’s peer-reviewed findings of carcinogenicity or to justify the FCC’s and ICNIRP’s thermal-based exposure limits.”

Joel M. Moskowitz, PhD, School of Public Health, University of California, Berkeley, whose research focuses on the public health implications of wireless radiation exposure:

“Millions of people carry cell phones against their bodies for hours a day, and children are being exposed over far longer lifetimes than any generation before them. Public health decisions about safety limits should be built on the most rigorous animal evidence available, not on studies constructed in a way that was unlikely to detect harm even if it exists. We cannot allow flawed experimental designs to shield outdated safety guidelines from necessary, health-protective revisions. The scientific evidence on cancer and other biological effects is sufficient to warrant policies to reduce exposure.”

Dr. Paul Héroux, Department of Epidemiology, Biostatistics and Occupational Health, McGill University:

“These studies did not reproduce the original methodology, exposure assessment, or study conditions. From a biostatistical perspective, testing only 70 animals at a single dose level leaves a study severely underpowered to detect rare carcinogenic events. Without multiple dose groups and adequate sample sizes, finding ‘no statistically significant effect’ is an artifact of poor study design rather than evidence of safety. Importantly, when the NTP and Korean and Japanese studies are considered together, the overall evidence confirms cancer risk.” 

Implications for Public Policy and Public Health

The authors state that governments have a responsibility to protect public health by ensuring that exposure limits are based on the strongest available scientific evidence, not on studies that lack the scientific rigor necessary to detect known hazards. They conclude that the Japanese and Korean follow-up studies cannot be relied upon to dismiss the U.S. National Toxicology Program’s findings or to delay protective action. Before negative validation studies can be interpreted as evidence against the NTP’s findings, they must match or exceed the original study’s design, including the same animal model, exposure regimen, adequate group sizes, multiple exposure levels, and sufficient statistical power. Accordingly, they state that the WHO’s International Agency for Research on Cancer (IARC) and regulatory agencies should base hazard evaluations and public health policies on the strongest available evidence.

ICBE-EMF maintains that current U.S. and ICNIRP exposure limits for cell phones, Wi-Fi, smart meters, and cell towers are not adequately protective because a substantial body of research reports cancer and other biological effects, including DNA damage, oxidative stress, neurological effects, and reproductive harm. The Commission calls on governments to halt the rollout of new wireless technologies until independent safety assessments are completed and to adopt policies that reduce RF radiation exposure risks.

Scientific reference:

Melnick, R.L., Moskowitz, J.M., Héroux, P. et al. Conflicting views in experimental carcinogenesis: a commentary on design and methodological deficiencies in the follow-up validation studies on radiofrequency radiation. Environ Health 25, 66 (2026). https://doi.org/10.1186/s12940-026-01324-5

About the ICBE-EMF 

ICBE-EMF is an international consortium of scientists, doctors, and researchers with expertise and peer-reviewed publications on the biological and health effects of electromagnetic fields, including RF radiation. The Commission is committed to upholding the highest standards of scientific research and makes science-based recommendations to ensure the protection of the public and the environment. 

https://icbe-emf.org/flawed-validation-studies-do-not-negate-the-established-evidence-that-cell-phone-radiation-causes-cancer-in-rats-scientists-conclude/


Conflicting views in experimental carcinogenesis: a commentary on design and methodological deficiencies in the follow-up validation studies on radiofrequency radiation

Melnick RL, Moskowitz JM, Héroux P, on behalf of International Commission on the Biological Effects of Electromagnetic Fields. Conflicting views in experimental carcinogenesis: a commentary on design and methodological deficiencies in the follow-up validation studies on radiofrequency radiation. Environ Health 25, 66 (2026). https://doi.org/10.1186/s12940-026-01324-5.

Abstract

Conflicting views in experimental carcinogenesis often arise due to differences in study design among reported studies. For carcinogenicity assessments, regulatory agencies, such as the US Food and Drug Administration (FDA), and intergovernmental advisory organizations, such as the Organization for Economic Co-operation and Development (OECD), specify the use of at least three dose levels plus control group for trend analyses, with the highest dose inducing a measurable toxic response. In addition, there needs to be a sufficient number of animals per group to have adequate power to detect a true carcinogenic effect. Departure from such recommendations can weaken the interpretations of study results. We examine here two recent carcinogenicity studies from Japan and Korea that were conducted following the positive carcinogenicity study of radiofrequency radiation (RFR) in experimental animals by the National Toxicology Program (NTP). The Japan and Korea follow-up studies used fewer animals per group, a single RFR exposure group, and a lower exposure level than the NTP study. Not surprisingly, while the NTP study revealed the carcinogenicity of RFR, the Japanese and Korean studies, which had reduced statistical power compared to the NTP study, issued conclusions conflicting with those of the more substantial NTP study on the health effects of RFR. In general, carcinogenicity studies with weaker doses, fewer exposure groups, and reduced statistical power should not be used to test the validity of more robust studies.

Excerpt

Despite the numerous limitations in their study design, the authors of the Japan-Korea studies concluded there is “no reproducible carcinogenic potential of mobile phone-type RF exposure in rats,” and that alternatives to the ICNIRP “recommend[ed] exposure limits for RF radiation based on thermal effects” are inconclusive [3]. These statements reflect ideological support for ICNIRP’s thermal-only mechanism of adverse effects and its repeated dismissal of the validity of the NTP carcinogenicity studies (e.g [12]). The project’s principal investigator is a member of ICNIRP, and the advisory committee that provided oversight and guidance throughout this project was heavily represented by current and past members of ICNIRP, suggesting a strong influence of ICNIRP in the design and interpretation of these studies.

In conclusion, methodological shortcomings due to the design choices in the Japan–Korea studies, specifically the restriction to a single exposure group of 4 W/kg of CDMA-modulated RFR and reduced statistical power, systematically biased the study toward null results and eliminated the possibility of detecting a positive trend. Consequently, these findings cannot be used to reasonably refute the peer-reviewed evidence of toxicity and carcinogenicity of CDMA- and GSM-modulated RFR in the NTP studies, nor to reinforce ICNIRP’s thermal-based exposure limits. It is also important to note that the increases in schwannomas and gliomas reported in experimental studies of RF-EMF are of the same tumor types (glioma and vestibular schwannoma) that were increased in epidemiological studies in which brain cancer risk was increased among heavy users of mobile phones [13]. The example described in this commentary demonstrates how limited and divergent experimental designs and potential biases in the interpretation of experimental carcinogenicity results can lead to conflicting views on the health effects of RFR.

Open access: https://link.springer.com/article/10.1186/s12940-026-01324-5

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The International Collaborative Animal Study of Mobile Phone Radiofrequency Radiation Carcinogenicity and Genotoxicity

Imaida K, Kawabe M, Wang J, Yokohira M, Imai N, Han K-H, Kim Y-B, Jeon SB, Kim HY, Ahn YH.The International Collaborative Animal Study of Mobile Phone Radiofrequency Radiation Carcinogenicity and Genotoxicity: The Japanese Study. Toxicol Sci. 2026. 1/13/26. https://doi.org/10.1093/toxsci/kfag002.

Abstract

The potential carcinogenic and genotoxic effects of radiofrequency electromagnetic fields, particularly those emitted by mobile communication systems, have raised public health concerns. A previous study by the U.S. National Toxicology Program suggested increased incidences of gliomas and cardiac schwannomas in rats exposed to high levels of RF radiation. To evaluate these findings, an international collaborative study was initiated between Japan and Korea.

Male Hsd:Sprague Dawley® SD® rats were exposed to 900 MHz CDMA-modulated RF-EMFs at a whole-body specific absorption rate of 4 W/kg for 18 hours and 20 minutes daily over two years. The study included a 28-day preliminary toxicity study, genotoxicity assays (alkaline comet and micronucleus tests), and a two-year carcinogenicity assessment. All procedures followed OECD guidelines and Good Laboratory Practice. No statistically significant increases in the incidences of neoplastic or non-neoplastic lesions were found in any major organ, including the brain, heart, and adrenal glands. Genotoxicity assays revealed no evidence of DNA damage or chromosomal aberrations in RF-exposed rats. A higher survival rate in the RF-exposed group, likely due to lower body weight and food consumption, was observed.

This study performed in Japan, jointly planned and executed by Japan and Korea, provides strong evidence that long-term exposure to 900 MHz RF-EMFs did not produce reproducible carcinogenic or genotoxic effects in male rats. Combined with data from the Korean counterpart study, these results are expected to contribute to future international assessments of the carcinogenic potential of electromagnetic radiation.

Open access: https://academic.oup.com/toxsci/article/209/3/kfag002/8423504

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The International Collaborative Animal Study of The Carcinogenicity and Genotoxicity of Mobile Phone Radiofrequency Radiation: The Korean Study

Kim HS, Han KH, Kim YB, Jeon SB, Lee AK, Moon JI, Choi HD, Imaida K, Yokohira M, Kawabe M, Imai N, Wang J, Ahn YH. The International Collaborative Animal Study of The Carcinogenicity and Genotoxicity of Mobile Phone Radiofrequency Radiation: The Korean Study. Toxicol Sci. 2026 Jan 16:kfag001. doi: 10.1093/toxsci/kfag001. 

Abstract

A chronic bioassay investigating radiofrequency (RF) carcinogenicity, intentionally designed to be conducted simultaneously in Korea and Japan, using the same research protocol and experimental environment. The study aimed to assess the potential carcinogenicity of Code Division Multiple Access (CDMA)-modulated 900 MHz RF signals at a whole-body specific absorption rate (SAR) of 4 W/kg, which is the reference level of the international human safety guideline, and to verify the key findings from the National Toxicology Program (NTP) study at that SAR level. Two reverberation chamber systems were used for RF exposures, and the same study protocols were followed. Male Harlan Sprague-Dawley (Hsd: Sprague Dawley® SD®) rats were randomly assigned to cage-control, sham-exposed, or RF-exposed groups. The exposure started on gestational day 5 and lasted for 18 hours and 20 minutes each day, with 10-minute on/off cycles. The project included a 28-day toxicity study, a 2-year carcinogenicity study, and a 14-week genotoxicity test. Histopathological evaluations were conducted in a partially blinded manner. The results were independently analyzed and submitted separately based on each country's research findings. In the Korean study, no statistically significant changes in tumor incidence or survival rates were observed. No significant RF-related effects were detected in the heart, brain, or adrenal glands. No changes in body temperature. Genotoxicity tests showed no evidence of DNA damage or mutation. In conclusion, the Korean part found that long-term exposure to CDMA-modulated 900 MHz RF was neither carcinogenic nor genotoxic at a SAR of 4 W/kg in male rats.

Open access: https://academic.oup.com/toxsci/article/209/3/kfag001/8428133

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An International Collaborative Animal Study of the Carcinogenicity of Mobile Phone Radiofrequency Radiation: Considerations for Preparation of a Global Project

Ahn YH, Imaida K, Kim YB, Han KH, Pack JK, Kim N, Jeon SB, Lee AK, Choi HD, Wang J, Kawabe M, Kim HS. An International Collaborative Animal Study of the Carcinogenicity of Mobile Phone Radiofrequency Radiation: Considerations for Preparation of a Global Project. Bioelectromagnetics. 2022 May;43(4):218-224. doi: 10.1002/bem.22407. 

Abstract

Radiofrequency radiation (RFR) was classified as a "possible" human carcinogen in 2011, which caused great public concern. A carcinogenicity study by the National Toxicology Program (NTP) found Code Division Multiple Access-and Global System for Mobile Communications-modulated mobile phone RFR to be carcinogenic to the brain and heart of male rats. As part of an investigation of mobile phone carcinogenesis, and to verify the NTP study results, a 5-year collaborative animal project was started in Korea and Japan in 2019. An international animal study of this type has two prerequisites: use of the same study protocol and the same RF-exposure system. This article discusses our experience in the design of this global study on radiofrequency electromagnetic fields (RF-EMFs).

Open access: https://onlinelibrary.wiley.com/doi/10.1002/bem.22407

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