The National Toxicology Program Study: $30 Million in Inconvenience

In 2018, the National Toxicology Program — a division of the U.S. Department of Health and Human Services — published the results of the most comprehensive investigation of radiofrequency radiation and cancer ever conducted. The study cost $30 million, took over a decade, exposed over 7,000 rats and mice to cell phone frequency radiation for up to two years, and produced findings that the NTP’s own peer review panel classified as “clear evidence of carcinogenic activity” for heart schwannomas and “some evidence” for brain gliomas in male rats. The Ramazzini Institute in Italy independently replicated the heart tumor finding at lower exposure levels. The FDA responded that the findings were not applicable to human cell phone use. The NTP’s cell phone radiation research program was subsequently defunded. No replacement program was announced.

The Study Design

The NTP study was designed to provide the definitive answer to a question that had been debated inconclusively for decades: does radiofrequency radiation at cell phone frequencies cause cancer? The study used the gold-standard methodology of toxicological research: large sample sizes (over 7,000 animals), whole-body exposure to eliminate dosimetry complications, multiple exposure levels (1.5, 3, and 6 W/kg SAR), two modulation types (GSM and CDMA, representing 2G and 3G technologies), two species (Hsd:Sprague Dawley rats and B6C3F1/N mice), both sexes, and exposure durations spanning the animals’ lifetimes (up to two years, equivalent to approximately 70 human years).

The exposure levels exceeded typical human cell phone use — the highest level (6 W/kg) is approximately four times the FCC’s limit for localized SAR from cell phones (1.6 W/kg). This is standard toxicological practice: carcinogenicity testing uses elevated doses to detect effects that might occur at lower doses over longer exposure periods in larger populations. Every known human carcinogen was identified through animal testing at doses exceeding typical human exposure. The methodology is not controversial in any other context.

The Findings

The NTP’s findings, as classified by an independent peer review panel of subject-matter experts convened specifically to evaluate the study, were:

“Clear evidence of carcinogenic activity” — the highest classification in the NTP’s four-level system — for malignant schwannomas (nerve sheath tumors) of the heart in male rats exposed to GSM- and CDMA-modulated RF radiation. The tumors appeared in a dose-dependent pattern: higher exposure levels produced more tumors. The tumors were of a type (schwannoma) that is rare in the control animal strain, making the finding statistically robust.

“Some evidence of carcinogenic activity” — the second-highest classification — for malignant gliomas (brain tumors) of the brain in male rats exposed to GSM- and CDMA-modulated RF radiation. Additionally, the study found increased DNA damage in multiple organs of exposed animals.

The Ramazzini Institute in Cesena, Italy — Europe’s largest independent toxicology laboratory — conducted a parallel study using lower exposure levels (0.001, 0.03, and 0.1 W/kg, approximating the levels experienced by people living near cell towers rather than using phones). Published in Environmental Research in 2018, the Ramazzini study found statistically significant increases in heart schwannomas in exposed male rats — the same tumor type, in the same tissue, as the NTP study. The independent replication of the finding at lower doses strengthened the evidence that the effect was real and dose-dependent.

The Institutional Response

The FDA — which had originally requested the NTP study — issued a statement that the NTP findings “should not be directly applied to human cell phone use” because the exposure levels were higher than typical use and the exposure was whole-body rather than localized. Both points are factually accurate. Neither addresses the underlying finding: radiofrequency radiation at cell phone frequencies produced tumors in controlled animal studies, in a dose-dependent pattern, replicated independently by a second laboratory at lower doses.

The NTP’s cell phone radiation research program was closed in 2022. The program’s resources were redirected to “other research priorities.” No replacement program investigating RF radiation and cancer was announced. No follow-up studies addressing the FDA’s specific criticisms (higher dose levels, whole-body vs. localized exposure) were commissioned.