The International Agency for Research on Cancer (IARC) at the World Health Organization (WHO) categorized in 2011 radiofrequency (RF) as a possible human carcinogen, Group 2B. During use of the handheld wireless phone, especially the smartphone, the thyroid gland is a target organ. During the 21st century, the incidence of thyroid cancer is increasing in many countries. We used the Swedish Cancer Register to study trends from 1970 to 2017. During that time period, the incidence increased statistically significantly in women with average annual percentage change (AAPC) +2.13%, 95% confidence interval (CI) +1.43, +2.83%. The increase was especially pronounced during 2010-2017 with annual percentage change (APC) +9.65%, 95% CI +6.68, +12.71%. In men, AAPC increased during 1970-2017 with +1.49%, 95% CI +0.71, +2.28%. Highest increase was found for the time period 2001-2017 with APC +5.26%, 95% CI +4.05, +6.49%. Similar results were found for all Nordic countries based on NORDCAN 1970-2016 with APC +5.83%, 95% CI +4.56, +7.12 in women from 2006 to 2016 and APC + 5.48%, 95% CI +3.92, +7.06% in men from 2005 to 2016. According to the Swedish Cancer Register, the increasing incidence was similar for tumors ≤4 cm as for tumors >4 cm, indicating that the increase cannot be explained by overdiagnosis. These results are in agreement with recent results on increased thyroid cancer risk associated with the use of mobile phones. We postulate that RF radiation is a causative factor for the increasing thyroid cancer incidence.
Keywords: NORDCAN; Nordic countries; RF-EMF; Swedish Cancer Register; cordless phone; incidence; ionizing radiation; mobile phone; radiofrequency electromagnetic fields; thyroid cancer.