Joel Moskowitz, from University of California-Berkeley (USA), and colleagues reviewed data from 23 case-controlled studies of cellular phone use, involving a total of 37.916 study subjects.  While a pooling of study data failed to reveal any significant increase in risk of brain tumors with cell phone use, the researchers did find a harmful effect in a subgroup of studies that used more rigorous study methodology.  In this study subset, researchers found that using a cell phone for ten years or more raised the risk of developing a brain tumor by 18%.  The team also warns cell phone users to be cautious for harm to other areas of the body, such as the heart or reproductive organs (when the phone is carried in an adjacent clothing pocket).