Thyroid cancer in children and young adults in the North of England. Is increasing incidence related to the Chernobyl accident?

Population-based data on thyroid carcinomas was obtained from the Northern Region Young Person's Malignant Disease Registry to analyse the incidence of thyroid cancers in young people (<25 years) in the North of England for the period 1968 and 1997 and to assess if changes in incidence were consistent with the spatial and temporal distribution of the fallout from the Chernobyl nuclear accident. We compared incidence rates for differentiated (papillary or follicular) thyroid carcinomas 1968-1986 with those for 1987-1997. There were 75 cases of thyroid carcinoma diagnosed over the study period, of which 63 were differentiated carcinoma and 12 were medullary carcinoma. There were 26 young adults (15-24 years) diagnosed with differentiated thyroid carcinoma in the 19-year period 1968-1986 and 30 in the subsequent 11 years 1987-1997, Age standardised rate (ASR) 3.0 versus 6.5, respectively (rate ratio 2.2, 95% confidence interval (CI): 1.3-3.6). There were three children (aged <15 years) diagnosed with differentiated carcinoma in the period 1968-1986 and four in the period 1987-1997, ASR 0.2 versus 0.6 (rate ratio 2.7, 95% CI: 0.6-12.1). Regression models showed a significant increase in the incidence of thyroid cancer after the Chernobyl accident (P=0.002). In Cumbria, the area receiving the heaviest fallout in the UK, the increase in incidence was much greater (rate ratio 12.19, 95% CI 1.5-101.2). These temporal and spatial changes in incidence are consistent with a causal association with the Chernobyl accident although a greater effect in the younger rather than the older age group would have been anticipated. However, factors including improvements in ascertainment and earlier detection of tumours may also have contributed to the increasing incidence. Further collaborative international studies are needed to investigate changes in the incidence of thyroid cancer in children and young adults.