The overall survival rate of thyroid
The overall survival rate of thyroid cancer has improved in parallel with the increasing incidence . The introduction of iodine therapy is among the improved treatment modalities for differentiated thyroid cancer . In Denmark, thyroid cancer is treated at highly specialized university centers based on a multidisciplinary collaboration between head and neck surgeons, oncologists, pathologists, nuclear physicians, endocrinologists, physicians, and radiologists. In Denmark, surgery is the primary choice of treatment for the various types of thyroid cancer; low-risk patients undergo hemithyroidectomy, whereas high-risk patients undergo total thyroidectomy and neck dissection (most often followed by treatment with radioactive iodine) .
Materials and methods All Danish citizens are issued with a unique personal identification (CPR)  which enables accurate individual GW311616 of data between registries. We included patients registered in the Danish Cancer Registry (DCR) diagnosed with a thyroid cancer between 1980 and 2014. The DCR was established in 1943 to ensure nationwide registration of all cancers. It has been mandatory to report to the DCR since 1987. Information on age at diagnosis, date of diagnosis, cancer location, and histology was derived from the DCR. Vital status (e.g. date of death or date of emigration) was obtained through linkage with the CPR. Patients were categorized into nine histological groups defined by the WHO in 2018  (Supplementary Table S1). This histological classification is adopted by the Danish National Guidelines and reflects the clinical approach to thyroid cancer nationwide. The study was approved by The Danish Data Protection Agency.
Discussion We demonstrated an increasing incidence of thyroid cancer explained primarily by an increase in papillary carcinomas. The incidence rates for papillary carcinomas quintupled from 1980 to 2014. Similarly, the national clinical thyroid cancer database, DATHYRCA , published a paper in 2013 on trends in papillary carcinomas between 1996 and 2008. The study found that the incidence rates increased by 50% during the investigated time period (1.43 per 100,000 to 2.16 per 100,000) . In comparison to this study, the AAIR for papillary carcinomas was 1.15 per 100,000 in 1996 and 1.79 per 100,000 in 2008. However, Londero et al.  did not report age-adjusted incidence rates, which possibly explains the observed differences. Thyroid cancer incidence rates are increasing in most developed countries . A retrospective analysis in the United States observed a nearly threefold rise in incidence rates from 4.56 per 100,000 person-years in the period 1974–1977 to 14.42 per 100,000 person-years in the period 2010–2013 . The explanation for this increase in incidence is controversial, and different causes have been hypothesized; increased diagnostic intensity (including immunohistochemistry and meticulous histopathological examination)[14,15], environmental and lifestyle changes [16,17], and ‘over-diagnosis’ – literally an epidemic of diagnosis . The more frequent and ubiquitous use of continuously advancing diagnostic procedures has increased the detection of many types of cancer. Specifically, the use of ultrasound, PET-CT scans, and cytology have identified an increasing number of small asymptomatic thyroid cancers, also named incidentalomas , which are found in up to 30% of autopsies . In particular, ultrasound has enhanced the detection of small thyroid nodules that would have gone undetected by physical examination in clinical practice. These small nodules constitute a potential reservoir of cancer lesions and are prevalent in up to 50% of the population in late adulthood ; this correlates with the observation that the greatest increase is among papillary microcarcinomas [16,17,22]. Other circumstances indicate that the observed increase is not due only to improved detection: primarily all sizes of tumors (> 1 cm) are increasing [16,17], and the increased incidence is not proportionately distributed for age or histology.