The increase in the number of thyroid carcinomas in children and adolescents has been observed since 1990, only 4 years after the Chernobyl accident, in southern Belarus and northern Ukraine, and from 1994 in southern Russia. In the Gomel region, the most contaminated area of Belarus, the incidence between 1986 and 1996 was 13/ 100 000 children/ year, compared to a baseline incidence of less than 1 per year. To date, more than 5000 cases of thyroid cancer have been reported among those who were children or adolescents at the time of the accident and living in the three most contaminated countries, Belarus, Ukraine, and Russia.
As shown in Figure1, most of the cases were registered in children below age 10 at the time of the accident, and nearly two- thirds in those younger than 5 years. Thyroid cancer cases have also been registered up to 20 years after the nuclear accident in children who were already conceived but still in utero, at that time. With respect to the 12 years before the accident, in the 12 years after the accident the increase of thyroid cancer in Belarus was 75- fold in children aged 3– 14 years at the time of diagnosis, 10.1- fold in adolescents (15– 18 years at diagnosis), 3.7- fold in young adults (19– 29 years), and 3.4- fold in adults (Table 1). This increase in adults is much less important than that observed in children and it is likely to be due to greater attention to thyroid diseases after the nuclear accident.
Fig1. Children and adolescents with post- Chernobyl thyroid cancer in Belarus (1500 cases diagnosed from 1986 to 2002).
Table1. Thyroid cancer in Belarus before and after the Chernobyl accident
Over 90% of the cancers were papillary. In the years following the accident most cancers were classified as a solid or follicular variant of papillary thyroid cancer, that is, the less frequently observed variant among naturally occurring papillary carcinomas. The clinical and pathological features were those of an aggressive tumour, as demonstrated by the histological appearance, the large size, the frequent multifocality and extracapsular invasion, and the frequency of node and lung metastases early in the course of the disease. However, later studies showed a decline over time in the proportion of the solid variant and an increase in the proportion of the classic variant. These changes correlated both with the increasing age and increasing latency period and it is not yet clear which of these two variables could be mostly responsible for these changing patterns, which are also associated with a change in the molecular features of these tumours.
The comparison between post- Chernobyl thyroid carcinomas diagnosed in Belarus and naturally occurring cases diagnosed in age- matched patients in Italy and France showed different clinical and epidemiological features. Post- Chernobyl tumours were much less influenced by gender (female: male ratio 1.6:1 versus 2.5:1 in Italy and France), were more advanced at presentation, were more frequently papillary, and were mainly diagnosed before age 15, while in Italy and France the majority were diagnosed after age 14.
As far as treatment and outcome are concerned, the available follow- up data indicate that post- Chernobyl thyroid carcinoma, when appropriately treated with a combination of total thyroidectomy, radioiodine, and hormone suppressive therapy, has the same favourable outcome as naturally occurring papillary cancer. Definitive cure is achieved in many patients, even in those with node and lung involvement, the quality of life is good, and the death rate does not exceed the usual 1– 2% reported in many series of paediatric thyroid cancer.
A similar observation has been recently reported in a study focused on external radiation- induced thyroid carcinoma. Although these tumours showed generally more aggressive features, the similar prognostic factors for their outcome indicate that they should be treated and followed in the same way as naturally occurring thyroid cancer.
