Thyroid cancer: zealous imaging has increased detection and treatment of low risk tumours

Summary box

• Clinical context—Thyroid cancer is the most common endocrine malignancy and one of the fastest growing diagnoses

• Diagnostic change—Introduction of neck ultrasonography into routine endocrinological practice in the 1980s with guided biopsy in the late 1990s, plus increased use of computed tomography and magnetic resonance imaging for other conditions

• Rationale for change—New imaging methods allow the detection and biopsy of thyroid nodules as small as 2 mm

• Leap of faith—Patients with small papillary cancers will benefit from their removal

• Increase in disease—Worldwide increase in incidence of thyroid cancer since the early 1980s but with considerable variation between countries. In the US the incidence of thyroid cancer has increased from 3.6 cases/100 000 population in 1973 to 11.6 cases/100 000 in 2009. Small papillary thyroid cancers, the most indolent form of thyroid cancer, account for 90% of cases

• Evidence of overdiagnosis—The expanding gap between the incidence of thyroid cancer and stable death rates from papillary thyroid cancer (0.5/100 000 in 1979 and 2009). Observational evidence shows that small papillary thyroid cancers, which are a common autopsy finding, may never progress to cause symptoms or death

• Harms from overdiagnosis—Patients having thyroidectomy experience physical complications, financial and psychosocial burdens, and need lifelong thyroid replacement therapy

• Limitations—Inference about overdiagnosis of thyroid cancer is based on epidemiological and observational evidence

• Conclusion – The incidence of small and indolent thyroid cancer is increasing, exposing patients to treatments inconsistent with their prognosis. We suggest a term that conveys the favourable prognosis for low risk thyroid cancers (micropapillary lesions of indolent course or microPLICs) and call for research to identify the appropriate care for these patients