Incidence, detection and outcome of differentiated thyroid cancer in Western Sweden.

Background: It is unclear whether the increasing incidence of thyroid cancer (TC) due to increased diagnosis of small and indolent tumours might mask a real increase of clinically significant cancers. The aim of this study was to correlate surgery, pathology and outcome data of individual patients to the mode of primary detection (palpation, by imaging or incidental) to assess if TC incidence has increased.

Methods: The Swedish Cancer Registry identified all patients with TC in Västra Götaland County representing approximately 1.6 million inhabitants. Clinical information was retrieved from medical records of patient cohorts from three study intervals (2001-2002, 2006-2007 and 2011-2014) comprising 60 per cent of all TC patients. Data were also obtained from the NORDCAN registry to compare of TC incidence with other Nordic countries.

Results: Between 2001 and 2014, the annualized standard incidence rate/100 000 population (ASR) of TC increased from 3.14 to 10.71 in women and from 1.12 to 3.77 in men. This was higher than the mean incidence for Sweden but similar to that in Norway and Finland. Differentiated TC (DTC) increased more than threefold. The majority of tumours (64 per cent) were detected by palpation. Larger tumours (10-20, 21-40 and greater than 40 mm) increased as much as microcarcinomas (less than 10 mm). Only 5 per cent of the tumours were detected by imaging. All disease-specific deaths (8.5 per cent of DTC in the first two cohorts) and most patients with recurrent or persistent disease (6.6 per cent of DTC cases) were diagnosed due to tumour-related symptoms.

Conclusion: DTC in Western Sweden gradually increased between 2001 and 2014. The majority of tumours were detected by palpation suggesting a real increase in the incidence of clinically significant thyroid malignancies.