Pathogenesis of thyroid cancer

Both epidemiological and molecular biological studies have been used to understand the origins of thyroid cancer. Epidemiological studies have been used to identify factors that predispose to thyroid cancer. That is principally how we know that exposure to radiation leads to thyroid cancer (see Chapter 3.2.5). In fact, radiation is the only environmental factor for which the proof is incontrovertible. Molecular biological studies, reviewed in the second part of this chapter, have been used to investigate the events within thyroid cells that are initiated by predisposing factors, e.g. radiation, and lead, by one or multiple steps, to transformation and cancer. These studies have focused on cancer-related genes, particularly proto-oncogenes and tumour suppressor genes, and have led to the identification of potential therapeutic agents. They have also focused on the cellular pathways and processes, including epigenetic changes and microRNA expression, which accompany transformation of the thyroid cell. Epidemiology and molecular biology have interacted productively in the studies that have followed the Chernobyl accident. This interaction is described in the third part of this chapter in which the mutations found in radiation-related thyroid cancers are reviewed.