The International Agency for Research on Cancer (IARC) has published a monograph that evaluates the carcinogenic hazard to humans of radiofrequency electromagnetic fields. The Working Group classified radiofrequency electromagnetic fields as possibly carcinogenic to humans (Group 2B).
IARC Monographs 102: Radiofrequency Electromagnetic Fields
More information on how IARC classifies carcinogens and the meaning of the ratings
