75% of Canadians diagnosed with thyroid cancer don't need aggressive treatment, new study suggests

Three out of four Canadians diagnosed with thyroid cancer don't require the aggressive treatment they get, an overdiagnosislikely due to the increased use of ultrasound imaging, suggests a new study published by University of Calgary researchers.

Doctors Dawnelle Topstad and James Dickinson say frequentthyroid testing, combined with improvements in imaging technology, are leading doctors to classify "clinically unimportant lesions" as cancer.

• Thyroid cancer often overdiagnosed, WHO's cancer arm says
• One-stop thyroid cancer clinic goal of Calgary doctors as rates increase

"Doing extra testing finds extra things, even when they're not important things," Dickinson, a professor at the Cumming Schoolof Medicine at the University of Calgary, said in an interview with CBC Calgary News at 6.

"If doctors find small thyroid cysts, they may diagnose it as a possible cancer even though the cysts would never grow, invade or spread."

Diagnosis rates jump, death rates unchanged

The study posted online by the Canadian Medical Association Journal on Monday finds that thyroid cancer diagnosis rates have jumped in recent years, whiledeath rates have remained stable, even though treatment protocols have remained unchanged.

• Read the full study, Thyroid cancer incidence in Canada: a national cancer registry analysis,here

Between 1970 and 2012, thyroid cancer incidence jumpedfrom 3.9 to 23.4 per 100,000 women, and from 1.5 to 7.2 per 100,000 men, according tothe National Cancer Incidence Reporting System and the Canadian Cancer Registry.

But mortality rates for both sexes haveremained stable at around 0.5 per 100,000 for both sexes, cites the study.

"If improved treatment for thyroid cancer is the reason for the mortality rates being constant, changes in treatment should coincide with the changing incidence. Despite debate over the past 40 years about the extent of surgery, the use of remnant radioactive iodine and suppressive thyroid hormone therapy, treatment protocols for thyroid cancer have not changed," write authors Topstadand Dickinson.

With a much greater incidence of thyroid cancer in women, treatment would need to be much more effective in women than in men for similar mortality rates to be observed in both sexes, write the authors.

But thyroid cancer treatment is identical for women and men.

The authors therefore conclude it is unlikely that more effective treatment explains the stable mortality rates.

'Something funny going on'

The authors estimate that at least 75 per cent of the people diagnosed with thyroid cancer do not need aggressive treatment.

That figure is based on the assumption that actual thyroid cancer rates today should be consistent with those observed in 1990, before ultrasound tests became readily available in Canada.

"We know of no cause [for the observed increase in thyroid cancer diagnosis]. All of the standard causes that we know of for thyroid cancer haven't really changed," Dickinson said.

Moreover, Dickinson said that, in countries that don't have readily available ultrasound testing,disease incidence rates remain the same.

The researchers also note that incidence rates varied widely between provinces and even between regions within a province from 1992 to 2012.

They could not identify any geographic risk factors that could explain these differences. Instead, the authors conclude the differences are "likely due to varying rates of overdiagnosis arising from differences in practice."

"There's something funny going on here, and it's got much more to do with the behaviour of doctors and patients than it has to do with disease," Dickinson said.

"It just doesn't make sense in terms of this distribution of disease, except in terms of how the healthcare system works or doesn't work."

Troubletelling which tumours are unimportant

Thyroid cancer treatment can include surgery and radioactive iodine (radioiodine) therapy, which have substantial side-effects and dangers. Post-surgery patients, for example, must take hormone treatments for life.

The authors say further efforts to reduce these negative consequences should aimto reducethe unnecessary use of diagnostic imaging.

They also say doctors must find better ways to distinguish between unimportanttumours and aggressive thyroid cancer that needs treatment.

According to Dickinson, doctors should be wary of performing tests that couldyield results suggestingaggressive therapy is needed when the cysts are extremely unlikely to grow, invade or spread. Andpatients need to start asking professionals whether prescribed tests are truly necessary.

Dickinson recommends that patients and doctorsfollow Canada's Choosing Wisely recommendations, which encourage conversations about unnecessary tests, treatments and procedures.

"Don't do thyroid scans unless you're feeling something, a lump, there. Don't do 'em just because you've got a slightly abnormal thyroid test."

• MORE ALBERTA NEWS |Brian Jean unveils plan to overhaul Alberta's health-care system
• MORE ALBERTA NEWS |Air quality level improves to low risk in Calgary area despite wildfire smoke