Thyroid cancer in Denmark 1943-2008, before and after iodine supplementation
A partir des données des registres danois du cancer et en analysant l'évolution de l'incidence du cancer de la thyroïde sur la période 1943-2008, cette étude évalue l'association entre une supplémentation en iode et le risque de cancer de la thyroïde
Thyroid cancer incidence has increased worldwide during the previous decades. In this nationwide study we aimed to identify the overall incidence of thyroid cancer in Denmark during 66 years (1943-2008) and incidences of the four main histological types of thyroid cancer from 1978 to 2008. Data were obtained from the nationwide Danish Cancer Registry, and we focused especially on the period after implementation of compulsory iodine supplementation, which was established on a national level in 2000. We calculated agestandardized incidence rates per 100,000 person–years and age–period–cohort–models were fitted to describe trends in incidence. To quantify trends in incidence over time, log–linear Poisson models were used to estimate annual percentage change. From 1943 to 2008 1947 men (29%) and 4682 women (71%) were diagnosed with thyroid cancer. The agestandardised incidence increased in both sexes; in men from 0.41 to 1.57 per 100,000 and from 0.90 to 4.11 per 100,000 in women, corresponding to a significant average annual percentage change of 1.7% and 1.8%, respectively. The incidence increased with younger birth cohorts. The rise was almost exclusively caused by papillary carcinomas, and it was particularly present during the last decades of the study period. It can not be ruled out that iodine supplementation may play a role for the risk of thyroid cancer, but as the strongest increase in incidence began in the years before the implementation, it is likely that improvement in diagnostic modalities, increased diagnostic activity and/or new unknown risk factors are also important contributors to the increase.