The World Health Organization, International Agency for Research on Cancer, has classified radiofrequency electromagnetic fields as possibly carcinogenic to humans (group 2B).
IARC Monograph 102, Non-Ionizing radiation part 2: radiofrequency electromagnetic fields http://monographs.iarc.fr/ENG/Monographs/vol102/mono102.pdf
Press Release here.
Lancet Oncology article here.