Participants will be followed annually according to the protocol of the GCS follow-up. Each subject will annually be contacted by a telephone call, and questions about the subject's vital status and cancer incidence will be asked from the subject or a first-degree relative. In addition, official data on subject's vital status will be obtained from the death registry unit in the Department of Health of Golestan University of Medical Sciences. Data on cancer incidence in the study subjects will also be obtained from the Golestan population-based cancer registry.