Increased incidence of thyroid cancer in Navarra (Spain). Evolution and clinical characteristics, 1986-2010

Introduction: The latest published studies show an increased incidence of thyroid cancer worldwide. The aim of this study was to analyze the changes in the incidence of thyroid cancer in Navarra and its clinical presentation regarding sex, histological subtype and size over the last 25 years.

Methods: Thyroid cancer incidence rates were calculated on the basis of data from the Cancer Registry of Navarra during 1986-2010. Clinical data were obtained from the historical cohort of the Hospital Registry of Cancer of Navarra, which includes all the new cases of differentiated thyroid carcinoma diagnosed and treated in the public health network of this Community in that period.

Results: The overall incidence of thyroid cancer in Navarra increased over the last 25 years, with an increase in the adjusted rate in men from 2.24 (1986-1990) to 5.85 (2006-2010) per 100,000 population/year (P<.001) and in women from 9.05 to 14.04, respectively (P<.001). This increase occurs only in papillary carcinoma. The clinical characteristics of 739 patients with differentiated thyroid cancer were studied. The mean age at diagnosis increased over the years and the predominance of women (about 80%) remains stable. Mean tumor size decreased over the five-year periods from 30.9 to 22.5mm (P<.001), the proportion of microcarcinomas (T1a) increased from 8.8% to 30% (P<.001) and, despite this increase, there were no statistical differences in the TNM stage at diagnosis during the study period. The distribution of histological variants of papillary and follicular carcinoma did not change over 25 years.

Conclusions: During the period studied, the incidence of thyroid cancer increased in Navarra in both sexes. The increase occurred only in papillary carcinoma, without changes in the distribution of his histological variants. The increase in the proportion of T1a tumors is remarkable, but the TNM stage distribution was maintained. These results suggest an increase in the diagnosis of thyroid microcarcinomas due to changes in clinical practice, without ruling out a real increase in the incidence of papillary carcinoma in Navarra.