INS and diabetes mellitus: By using the population-based reimbursement database of the National Health Insurance (NHI) of Taiwan, the aims of the present study were to evaluate 1) whether diabetic patients might have an increased risk of thyroid cancer in terms of diabetes status and diabetes duration; and 2) whether the anti-diabetic drugs, including insulin, sulfonylurea, metformin, acarbose, pioglitazone and rosiglitazone, might be associated with thyroid cancer.