Thyroid Ultrasound and the Increase in Diagnosis of Low-Risk Thyroid Cancer

Context: Thyroid cancer incidence increased with the greatest change in adults aged 65 years. Objective: To determine the relationship between area-level use of imaging and thyroid cancer incidence over time. Design, Setting and Participants: Longitudinal imaging patterns in Medicare patients aged 65 years residing in Surveillance, Epidemiology, and End Results (SEER) regions were assessed in relationship to differentiated thyroid cancer diagnosis in patients aged 65 years included in SEER-Medicare. Linear mixed-effects modeling was used to determine factors associated with thyroid cancer incidence over time. Multivariable logistic regression was used to determine patient characteristics associated with receipt of thyroid ultrasound as initial imaging. Main Outcome Measure: Thyroid cancer incidence. Results: Between 2002 and 2013, thyroid ultrasound use as initial imaging increased (P < 0.001). Controlling for time and demographics, use of thyroid ultrasound was associated with thyroid cancer incidence (P < 0.001). Findings persisted when cohort was restricted to papillary thyroid cancer (P < 0.001), localized papillary thyroid cancer (P = 0.004), and localized papillary thyroid cancer with tumor size 1 cm (P = 0.01). Based on our model, from 2003 to 2013, at least 6594 patients aged 65 years were diagnosed with thyroid cancer in the United States due to increased use of thyroid ultrasound. Thyroid ultrasound as initial imaging was associated with female sex and comorbidities. Conclusion: Greater thyroid ultrasound use led to increased diagnosis of low-risk thyroid cancer, emphasizing the need to reduce harms through reduction in inappropriate ultrasound use and adoption of nodule risk stratification tools.