Clinical presentation and clinical outcomes in Chernobyl-related paediatric thyroid cancers: what do we know now? What can we expect in the future?

Over the last 20 years, nearly 5000 cases of differentiated thyroid cancer have been diagnosed and treated in the regions of Russia, Ukraine and Belarus in young people previously exposed to the Chernobyl radioactive fallout during childhood. At diagnosis, 60-70% of the Chernobyl-related paediatric thyroid cancers had clinically evident cervical lymph node metastases (N1) and 10-15% had distant metastases (M1). Despite early reports suggesting that the paediatric thyroid cancer cases that developed after exposure to Chernobyl fallout were particularly aggressive, it now seems that the initial presentation and early clinical course of most of these cases are very similar to both non-radiation-associated paediatric thyroid cancers and thyroid cancers that arise after exposure to external beam irradiation. Over an average clinical follow-up period of about 10 years, the disease-specific mortality rate in these paediatric thyroid cancer cases that developed after the Chernobyl accident is quite low (1% or less). As would be expected in paediatric thyroid cancer, short-term recurrence rates range from 7 to 28% in published reports (mean 17%). However, long-term studies of paediatric thyroid cancer suggest that although the 30 year disease-specific mortality rate should be about 1%, the risk of developing structural disease recurrence is nearly 30% (of which 80% are expected to be locoregional recurrences and 20% are probably new distant metastases). Projected over 30 years of follow-up, a 1% disease-specific mortality in this cohort of 5000 patients would equate to about 50 deaths directly attributable to thyroid cancer. However, a 30% recurrence rate would also mean that about 1500 patients may develop a clinically meaningful recurrence that would need to be diagnosed and treated. It is imperative that we continue to work with our colleagues in Belarus, Ukraine and Russia to ensure that this large volume of patients destined to develop clinically significant recurrences are diagnosed and treated in a timely manner. Ready access to modern disease detection tools (serum thyroglobulin, postoperative neck ultrasonography, cytology/pathology support, and radioactive iodine scanning) and treatments (surgery for recurrent disease, radioactive iodine therapy) in their major academic centres are mandatory if we expect to achieve the excellent clinical outcomes that should be seen when paediatric thyroid cancer recurrence is diagnosed early and treated appropriately.