Aetiology

Low dose radiation may be an important factor as many cases have been reported 10-30 years after X-ray exposure.

• radioiodine - there is evidence that individuals treated with radioiodine have a small but significant increase in the incidence of thyroid cancer (1).
• a history of radiation exposure to the neck area is associated with increased risk of thyroid cancer, often after a delay of well over a decade; some cases can be traced to radiation treatment in childhood (2)

Both deficiency and excess dietary iodine are associated with increased risk of thyroid cancer (2)

Other predisposing factors include (2):

• prolonged stimulation with thyroid stimulating hormone (which can be due to chronic iodine deficiency)
• chronic lymphocytic thyroiditis (lymphoma)
• genetic factors (linked with medullary thyroid cancer)
• women are more than twice as likely as men to develop thyroid cancer

Reference:

1. Franklyn JA, Maisonneuve P, Sheppard MC et al (1999). Cancer incidence and mortality after radioiodine treatment for hyperthyroidism: a population-based cohort study. Lancet; 338 (11): 712-718.
2. NICE (November 2004). Improving outcomes in head and neck cancers - The Manual