Thyroid cancers overdiagnosed in Canada for in 75 percent of patients

A new study by a University of Calgary researcher reveals 75 per cent of Canadians diagnosed with thyroid cancer don't have it.

"There's been a dramatic escalation of thyroid cancers in the last 40 years for no apparent cause," says lead author Dr. James Dickinson, who worked with surgeon Dr. Dawnelle Topstad on the research published in the journal CMAJ Open.

The research findings fit the idiom of "too much of a good thing" becomes harmful. Several decades ago, the only thyroid cancers to be diagnosed were lumps doctors could feel with their hands. Since then, improvements in modern imaging technologies such as ultrasound, CT and MRI have unlocked the possibility of detecting tiny cysts in the thyroid. While some are early cancers, others grow very slowly or not at all, and would not cause problems if left alone, explains Dickinson.

"It's really a terrible thing to do to somebody, to tell them they have cancer if there's no medical reason to diagnose as cancer and treat," the researcher says. "Calling something a cancer can change a person's life forever, forcing sometimes life-changing choices."

Five- and six-fold increase in thyroid cancer incidence rates in Canada

The study found that thyroid cancer incidence rates increased in Canada by five and six times in men and women respectively between 1970 and 2012 with unchanged mortality rates. The researchers also examined outcomes for patients who were diagnosed with thyroid cancer and found that there was no decrease in death rates from the disease. In other words, although more people have been diagnosed and treated for thyroid cancer over the last 40 years, this made no change to their outcomes.

The study also found no biological cause that would lead to an increase in incidence rates other than the availability of modern ultrasound machines. The data was obtained from The National Cancer Incidence Reporting System and the Canadian Cancer Registry.

Dickinson and Topstad concluded the increase is likely an overdiagnosis epidemic. "It's a good thing to have modern technology at our hands to help us diagnose, but it causes a lot of harm to people if ultimately we are treating patients who would be better served not being diagnosed at all," says Dickinson. "We as doctors need to get a lot better at clarifying which ones are true cancers; without this clarity many patients are put through unnecessary heartache and worry, even harm."

A better option is to distinguish patients with unimportant tumours

If patients undergo surgery to remove a thyroid gland, they will then receive hormone replacements for the rest of their life. "We should concentrate on finding better ways to distinguish patients with unimportant indolent tumours, while still identifying aggressive thyroid cancers that need treatment," says Dickinson. "We're just treating a lot more patients and getting no improvements in health outcomes."