Comparison of 2018 NTP Studies and 2025 DTT Pilot Studies
| 2018 NTP Studies | 2025 DTT Pilot Studies |
Purpose | Comprehensive evaluation of cancer and DNA damage risks from long-term cell phone radiofrequency radiation exposure in male and female rats and mice | Mechanistic follow-up to explore possible biological pathways for tumor and DNA damage seen in the 2018 NTP study in male and female rats and male mice |
Exposure Duration
| 14 to 19 weeks for DNA genotoxicity tests 2 years for carcinogenicity study
| 5 days for DNA genotoxicity tests |
Pre-natal Exposure | Yes, for male and female rats, studies began on gestation day 6. No, for male mice, 5-6 weeks old on first day of study. | No, male rats were 28–31 weeks old, female rats were 23 weeks old, and male mice were 33 weeks old on first day of study. |
Cancer | Increased tumors in male rats: Clear evidence of cancer in the heart (malignant schwannoma) Some evidence of cancer in the brain (malignant glioma) Some evidence of tumors in the adrenal glands (benign, malignant, or complex combined pheochromocytoma)
| Did not test for cancer |
DNA Damage | Significant increases in DNA damage in:
the hippocampus of male rats, the frontal cortex of the brain in male mice, and the blood cells of female mice.
| Although report concluded RFR exposure for 5 days did not induce DNA damage, the studies found significant increases in DNA damage in:
the hippocampus of male rats, the frontal cortex of the brain in female rats, and the liver in male mice.
|
Related posts:
National Toxicology Program (NTP) Finds Cell Phone Radiation Causes Cancer
==
Cell Phone Radiation Follow-up Studies
NIEHS, August 7, 2025
"NIEHS scientists in the Division of Translational Toxicology,
which supports the NTP, undertook research to better understand some of
the findings seen in the earlier RFR rodent studies reported in NTP
Technical reports TR-595 and TR-596.
They designed and developed a novel custom small-scale RFR exposure
system, which included building, testing, and validating the exposure
system. This new exposure system was based on the system used in the
published NTP rodent studies. Researchers then conducted a series of
short-term in vivo rodent studies.
NIEHS has completed the follow-up studies with this small-scale RFR
exposure system. The results from these follow-up studies are published
in a peer-reviewed report posted on the NIEHS website (see sidebar).
The research using this small-scale RFR exposure system was
technically challenging and more resource intensive than expected. In
addition, this exposure system was designed to study the frequencies and
modulations used in 2G and 3G devices, but is not representative of
newer technologies such as 4G/4G-LTE, or 5G (which is still not fully
defined). Taking these factors into consideration, no further work with
this RFR exposure system will be conducted and NIEHS has no further
plans to conduct additional RFR exposure studies at this time."
RFR Follow-up Studies
--
Development and testing of a novel whole-body exposure system for
investigative studies of radiofrequency radiation in rodents
Wyde ME, Capstick M, Hall SM, Hooth MJ, Kuster N, Ladbury JM, Roberts
GK, Shipkowski KA, Shockley KS, Smith-Roe SL, Stout MD, Walker NJ. 2025.
Development and testing of a novel whole-body exposure system for
investigative studies of radiofrequency radiation in rodents. Research
Triangle Park, NC: National Institute of Environmental Health Sciences. [https://doi.org/10.22427/NIEHS-RFR]
Executive Summary
"The predominant source of human
exposure to radiofrequency radiation (RFR) occurs through the use of
cell phone handsets. Previous toxicology studies on RFR, conducted in
support of the National Toxicology Program (NTP) by researchers at the
National Institute of Environmental Health Sciences (NIEHS), found
exposure-related effects on body temperature and DNA damage. The studies
reported herein were conducted by NIEHS researchers in the Division of
Translational Toxicology to better understand the biological mechanisms
that produced tumor development and DNA damage in exposed rodents. These
studies were not conducted as part of the NTP.
The goals of the
current research were to design, construct, and use a small-scale RFR
exposure system to conduct toxicological research in rats and mice. One
of the primary specific objectives of this research was to test and use
new, experimental methods to collect physiological data from animals in
real time during RFR exposures, including assessment of body temperature
and use of videos for clinical observations. Previously, such data
collections were not feasible without cessation of RFR exposure.
A
new RFR exposure system based on the technical parameters of the system
used in the previous NTP toxicology and carcinogenesis studies was
developed for small-scale investigative studies with fewer animals. The
system was designed with enhanced capabilities and more flexibility,
including the ability to generate additional radiofrequency (RF) signals
with frequencies and modulations used in more current wireless
communication technologies. After development and installation, the
system was rigorously tested and independently verified before animal
studies were conducted. Following completion of the mouse study, several
system modifications were required before the rat studies could be
conducted. These system modifications required significant technical
expertise and sometimes took several months to resolve successfully.
A series of 5-day studies was conducted in male or female Sprague Dawley (Hsd:Sprague Dawley® SD®)
rats or B6C3F1/N mice to evaluate the effect of exposure to the same
Code Division Multiple Access (CDMA)- or Global System for Mobile
Communications (GSM)-modulated RF signals used in the previous NTP
studies. Video from the cameras in the exposure chambers demonstrated no
visible response in either rats or mice at the first time the exposure
system was activated, at subsequent system on/off transitions, or during
the periods of exposure. Exposure to RFR for 5 days did not induce DNA
damage in brain cells (frontal cortex, hippocampus, and cerebellum), or
in liver, heart, or blood cells of rats and mice, as measured using the
comet assay. These investigative studies of RFR exposure were
technically challenging to conduct and, unfortunately, measurement by
two different methods did not yield data useful for assessing body
temperature during exposure.
Despite a number of difficulties
(i.e., engineering requirements, system modifications, measurement of
body temperature during exposure), this small-scale RFR exposure system
presents a prototype for investigative toxicological studies by
researchers interested in conducting experimental RFR studies in rodent
models. High-quality studies to understand the effects of RFR exposure
on biological responses are needed given the widespread human exposure
to RFR associated with cell phone use. The aim of this report is to
share knowledge and facilitate advancement in research methodologies for
investigating the potential health effects of RFR."
Excerpts
"In
the current studies, male rats were exposed to CDMA or GSM-modulated
RFR, and female rats and male mice were exposed to CDMA-modulated RFR."
"Based
on the homogeneity results of previous analyses that modeled the
specific absorption rate (SAR) distribution of RFR across the whole
body, rats were exposed at a frequency of 900 MHz, and mice were exposed
at 1,900 MHz."
"While reviewing videos captured during exposure
(see Section 4.2.3.5), it was noted that the stirrer on the back wall of
the control chamber (Chamber 4) did not move throughout the
four experiments (male mouse CDMA, male rat CDMA, female rat CDMA, male
rat GSM)."
"The signal generator (SMBV-100A, Rhode & Schwarz,
Germany) chosen was capable of generating the types of signals used in
the previous NTP RFR studies."
"These chambers and the studies
described in Section 4.2 utilized a 10-minute on/10-minute off
alternating exposure paradigm by which animals in each chamber were
exposed for 9 hours and 10 minutes per day over an 18-hour and 20-minute exposure period."
"An
RFR field exposure system was designed to enable equivalent exposure
conditions to those utilized in the previous NTP 2-year studies and for a
smaller number of animals with a smaller facility footprint."
Figure 3: The mouse CDMA study was conducted in July 2020. The rat studies were conducted from September to November 2021.
"During
the acclimation period, prior to the start of exposure, it was
discovered that the rats were able to chew through the cage filter tops
and escape their cage units."
"After system installation, verification, and qualification were
completed, a series of four 5-day studies was conducted in Sprague
Dawley (Hsd:Sprague Dawley ® SD®) rats or B6C3F1/N mice. The goal of
these studies was to further characterize radiofrequency radiation
(RFR)-induced changes in body temperature and DNA damage observed in the
previous National Toxicology Program (NTP) RFR studies and evaluate the
use of new methods for collecting live, real-time data."
"On the
first day of the studies, rats were approximately 28–31 weeks (male) or
23 weeks (female) old, and male mice were approximately 33 weeks old.
Rats and mice were randomly assigned to one of five exposure groups
before the start of the study. Randomization was stratified by body
weight that produced similar group mean weights using NTP Provantis
software (Instem, Stone, UK)."
"Groups of 10 male and 10 female
rats and 10 male mice were housed individually in reverberation chambers
and exposed to whole-body RFR via Code Division Multiple Access (CDMA)
(Interim Standard 95 [IS-95], 1,900 MHz) or via Global System for
Mobile Communications (GSM) single modulation (900 MHz)."
"These
studies were conducted under the NIEHS contract with Battelle Memorial
Institute (HHSN273201400015C). The studies were initiated at the
Battelle testing facility in West Jefferson, Ohio. On May 1, 2021, the
testing facility was transferred to a new company, AmplifyBio....For the
mouse study, all of the in-life, postmortem, and analytical portions of
the study were conducted while Battelle was the testing facility;
reporting was conducted under AmplifyBio as the testing facility. The
rat studies were conducted under AmplifyBio as the testing facility."
"Body temperature data were unusable because of data quality or data collection issues."
"There were no exposure-related effects on survival or body weights
with CDMA-modulated RFR exposure up to 9 W/kg for 5 days in male rats."
"There
were no exposure-related effects on body weights with GSM-modulated RFR
exposure up to 9 W/kg for 5 days in male rats. On study day 5, body
weights showed a negative trend and a significant decrease in the 6 W/kg group compared to the chamber control group."
"Statistical methods were chosen based on distributional assumptions. Unless specifically mentioned, all endpoints were tested for a trend across exposure groups, followed by pairwise tests for each exposed group against the chamber control group. Significance of all trend and pairwise tests is determined by a p value of ≤0.05 and is reported at both 0.05 and 0.01 levels. The room control group was analyzed only by a single pairwise comparison to the chamber control group. The room control analysis was kept separate from that of the other exposed groups and was excluded from all trend tests."
DNA
damage from exposure to RFR was assessed in frontal cortex,
hippocampus, cerebellum, liver, blood, and heart cell samples from male
mice and male and female rats using the comet assay (Table D-1, Table
D-2, Table D-3, and Table D-4). For CDMA male mice,
there were no significant increases in DNA damage, measured as the
percent tail DNA, in cells sampled from the three brain regions, blood,
and heart tissue; there was a significant trend test for the percent tail DNA in liver cells that is of uncertain biological significance. For CDMA male and CDMA female rats, no
significant increases in the percent tail DNA were observed for any
tissue. For GSM male rats, there were no significant increases in DNA
damage, measured as the percent tail DNA, in cells sampled from frontal
cortex, cerebellum, liver, blood, or heart tissue; there was a significant trend test for the percent tail DNA in hippocampal cells that is of uncertain biological significance.
4.4 Summary: "Five-day studies were conducted in male mice or male or
female rats to evaluate the effect of exposure to the same CDMA- or
GSM-modulated RF signals used in the previous NTP studies. Video from
the cameras in the exposure chambers demonstrated no consistent,
exposure-related, and visible changes in activity in either rats or mice
the first time the exposure system was activated, at subsequent system
on/off transitions, or during the periods of exposure. There were no
exposure-related effects on survival or body weights following exposure
to RFR for 5 days. There was no increase in DNA damage following
exposure to RFR for 5 days, as measured using the comet assay, in brain
cells (frontal cortex, hippocampus, and cerebellum), or in liver, heart,
or blood cells of mice and rats. Body temperature measurements were
collected during the studies using two different devices; however, the
data were unusable."
Conclusions
"The studies reported
herein were conducted by researchers in the Division of Translational
Toxicology (DTT) at the National Institute of Environmental
Health Sciences (NIEHS). These studies were not conducted as part of the
National Toxicology Program."
"The new small-scale RFR exposure
system described in this report was developed by NIEHS/DTT to overcome
those limitations with a signal generator capable of generating a
broader array of RF signals. In addition to the GSM and CDMA signals at
900 and 1,900 MHz used in the previous NTP studies, the small-scale
exposure system could generate signals reflective of more current
wireless communications (e.g., Third Generation Partnership Project
[3GPP] LTE Frequency Division Duplex [FDD] and Time Division Duplex
[TDD], LTE-Advanced, 3GPP FDD/ High-Speed Packet Access [HSPA]/HSPA+,
GSM/Enhanced Data rates for GSM Evolution [EDGE]/EDGE Evolution, Time
Division-Synchronous CDMA [TD-Whole-body Radiofrequency Radiation
SCDMA], Wireless Local-area Network [WLAN]) with frequencies between 9
kHz and 3.2 GHz, modulations with base bandwidths of up to 120 MHz, and
carrier frequencies of up to 3,200 MHz."
"In these studies,
evaluation of video from the cameras in the exposure chambers
demonstrated no consistent, exposure-related, and visible changes in
activity in either rats or mice the first time the system was activated,
during subsequent system on/off transitions, or during the periods of
exposure."
"Equivocal results,
showing limited statistically significant effects, were observed for
male mouse liver cells (CDMA) and male rat hippocampal cells (GSM) in
these 5-day studies. Although it is not possible to directly compare the
5-day and 90-day comet assay studies, it is interesting to note that a
positive result for hippocampal cells from male rats exposed to CDMA was
observed in the 90-day study."
"High-quality
studies to understand the effects of RFR exposure on biological
responses are needed given the widespread human exposure to RFR
associated with cell phone use."
Excerpts from tables with statistically significant tests of trends for DNA damage
Table D-1. DNA Damage in Male Mice Exposed to Whole-body CDMA-modulated Cell Phone Radiofrequency Radiation for Five Days
Open access report: https://www.niehs.nih.gov/sites/default/files/2025-08/cellphonerfr_long_508.pdf