Letter to the editor.

Some have looked forward to the publication of the results of the COSMOS study on brain tumors, because the potential biases from retrospective investigations predominating the search for brain tumor risks of mobile phone use since the late 1990 s were deemed unresolvable by further investigations of that type. Indeed, prospective cohort studies typically have the advantage of being not or less affected by differential exposure misclassification, recall and selection bias, and, as they proceed in the direction of the time arrow, results are more easily interpreted in terms of causation. However, results of the COSMOS study published now in this journal are not of help for the risk assessment of mobile phone use and do not support the conclusions of the authors that their findings "suggest that the cumulative amount of mobile phone use is not associated with the risk of developing glioma, meningioma, or acoustic neuroma".