The thyroid cancer "epidemic" in 12 developed countries is largely due to diagnosis of tumours that are very unlikely to cause symptoms or death, say researchers who call for curbs on unnecessary surgery.



Investigators from the International Agency for Research on cancer (IARC) used cancer registry data from 12 countries to estimate overdiagnosis of thyroid cancer.



In Thursday's issue of the New England Journal of Medicine, they estimated that more than 470,000 women and 90,000 men in those countries may have been overdiagnosed with thyroid cancer over 20 years.

The vast majority of people who were overdiagnosed with thyroid cancer underwent "very heavy treatment," said study author Salvatore Vaccarella of the Lyon, France-based IARC.



"We need to think that these people would have lived a very normal life without any symptoms and without any reduced life expectancy compared to the general population," he added in an interview from Venice.

The data so far is highly suggestive that in most cases these cancers if left alone will do fine without treatment. - Dr. Ali Imran





Vaccarella called it the first study to quantify such a massive suspected effect of overdiagnosis of thyroid cancer in developed countries. He attributes it to the introduction of ultrasound, CT and MRI diagnostic techniques to detect small, symptomless lesions in the thyroid gland.



He suggests:

Less screening for thyroid cancer.

Low-risk tumours could be reclassified as something other than "cancer" to avoid scaring people.

Watchful waiting for patients with low-risk nodules less than one centimetre in size.

The concern is well-known, said Dr. Ali Imran, a professor of medicine in the endocrinology division at Dalhousie University in Halifax. He was not involved in the report.

"The issue is that we don't know with absolute certainty the long-term outcomes of such small thyroid cancers that are picked through ultrasounds," Imran said in an email.

"The data so far is highly suggestive that in most cases these cancers if left alone will do fine without treatment. In fact many autopsy studies show a signification proportion of individuals dying of unrelated reasons harbour small thyroid cancers."

An alarming diagnosis

Doctors discovered a four-centimetre mass on Deana Ruston's thyroid when an orthopedic surgeon ordered an MRI for scoliosis or curvature of the spine.



"Unfortunately it was quite advanced by the time it was discovered," the 24-year-old from London, Ont., recalled.



Waiting for the surgery was the hardest part, Ruston said.



"I agree with calling it 'not cancer,'" she said. "It definitely makes people panic. Hearing the word cancer is very loaded."



Doctors are now watching a second, smaller growth on the right side of Ruston's neck.

Historically, thyroid cancer affects more women than men, perhaps because women are more likely to seek out medical attention earlier, Vaccarella said.