Abstract
Worldwide, the incidence of thyroid (TC)cancer has increased over the past few decades; however, the cause has been debated. Several theories have been proposed to explain this. Some have addressed over-detection and others have focused on the growing number of clinically relevant cases being detected and the possible increase in risk factors exposure. This study reviewed the possible reasons for the increase in the TC incidence rate, to determine the existence of a true increased incidence, to clarify the role of overdiagnosis and to elucidate the possible risk factors for TC.Articles in the following databases were systematically reviewed: Medline, the Cochran Library, CINAHL and Embase. The increase in incidence of TC over the past several decades has been well documented. The reviewed studies attributed the rise mainly to overdiagnosis, due to improved access to health care, and thedevelopment of higher-quality diagnostic techniques. However, a parallel increase in risk factors exposure and the increased incidence of clinically significant TC cases especially papillary type have been documented, which suggest a true increase of TC incidence rate.The surge in the TC incidence rate seemed to be multifactorial. It cannot be attributed to over diagnosis as a sole cause.