They determined there is “clear evidence” that male rats exposed to high levels of radio frequency radiation — typical of 2G and 3G networks when the study was designed — developed heart schwannomas. There was also “some evidence” of brain and adrenal gland tumors, again in the male rats, but the exposed female rats, and male and female mice, did not have consistent patterns of disease.

Can cellphone radiation cause cancer in humans? There’s no scientific consensus on this issue, but there is “some evidence” that exposure to radiation equivalent to that emanating from 1990s-era cellphones is associated with brain tumors in male rats, according to results of a US National Toxicology Program (NTP) study released last week (November 1). 
Radiofrequency radiation is a form of electromagnetic radiation. Electromagnetic radiation can be categorized into two types: ionizing (e.g., x-rays, radon, and cosmic rays) and non-ionizing (e.g., radiofrequency and extremely low frequency, or power frequency). Electromagnetic radiation is defined according to its wavelength and frequency, which is the number of cycles of a wave that pass a reference point per second. Electromagnetic frequencies are described in units called hertz (Hz).