Rates of thyroid cancer in England have doubled in the last two decades, a study has shown.
One possible cause of the trend could be radiation treatment for other forms of cancer, say researchers.
Radiation is a known risk factor for thyroid cancer, along with faulty genes, low iodine levels and poor diet.
The 1986 Chernobyl nuclear disaster in the Ukraine led to a dramatic increase in thyroid cancer cases among children living in the affected area.
Between 1990 and 1994 around 900 people were diagnosed with thyroid cancer each year in England, an incidence of 1.7 per 100,000.
By 2006-10 this figure increased to 1,950 (3.4 per 100,000 people), according to the new report published by the National Cancer Intelligence Network (NCIN).
Thanks to effective treatments, survival rates have remained high, at around 90%.
Researchers from the Oxford Cancer Intelligence Unit found that most of them involved a relatively benign type of disease called papillary cancer.
David Chadwick, consultant endocrine surgeon at Chesterfield Royal Hospital and chair of the NCIN Thyroid Working Group, said: “The exact reason behind this steep rise in thyroid cancer cases remains unclear.
“We now have more sensitive diagnostic techniques, so it could be that more cancers are being picked up when patients are being tested for other conditions.
“This could mean that we’re detecting and treating some cancers that would otherwise not have shown up during a person’s life.
“We may also be seeing a ‘real’ increase in the incidence of thyroid cancer, some of which may be due to improved long-term survival of other cancers previously treated with radiotherapy to the neck or chest.
“Sadly, older forms of radiotherapy had a side-effect that increased the risk of other cancers later in life.”
New diagnostic techniques include ultrasound and fine needle biopsies that can pick up much smaller cancers.
The report also showed that thyroid cancer is three times more common in women than in men.
For both sexes, one-year survival rates had increased, to 88.3% for men and 94.3% for women.
Thyroid cancer is most often diagnosed in people aged between 20 and 59.
Treatment commonly includes surgery to remove the thyroid and is often followed up with radioactive iodine. This acts as a ‘targeted’ treatment as the iodine is only taken up by thyroid cancer cells, ultimately killing them.
Some forms of thyroid cancer have a very poor prognosis, but the future behaviour of the disease is hard to predict in the early stages.