Abstract
BACKGROUND: Controversy exists over whether there has been a true increase in the occurrence of thyroid cancer or overdiagnosis secondary to imaging practices. Because cancer overdiagnosis is associated with detection of indolent disease, overdiagnosis can be associated with perceived improvement in survival. MATERIALS AND METHODS: Surveillance, Epidemiology, and End Results-Medicare linked database was used to determine the relationship between type of imaging leading to thyroid cancer diagnosis and survival. Disease-specific and overall survival were evaluated in 11,945 patients aged ≥66 years with differentiated thyroid cancer diagnosed between January 1, 2001, and September 30, 2015, who prior to their cancer diagnosis initially underwent thyroid ultrasound versus other imaging capturing the neck. Analyses were performed using the Kaplan-Meier method and Cox proportional hazards model with propensity score. RESULTS: Patients who underwent thyroid ultrasound as compared with other imaging had improved disease-specific and overall survival (p < .001, p < .001). However, those who underwent thyroid ultrasound were less likely to have comorbidities (p < .001) and more likely to be younger (p < .001), be female (p < .001), have localized cancer (p < .001), and have tumor size ≤1 cm (p < .001). After using propensity score analysis and adjusting for tumor characteristics, type of initial imaging still correlated with better overall survival but no longer correlated with better disease-specific survival. CONCLUSION: There is improved disease-specific survival in patients diagnosed with thyroid cancer after thyroid ultrasound as compared with after other imaging. However, better disease-specific survival is related to these patients being younger and healthier and having lower-risk cancer, suggesting that thyroid ultrasound screening contributes to cancer overdiagnosis. IMPLICATIONS FOR PRACTICE: The findings from this study have implications for patients, physicians, and policy makers. Patients who have thyroid ultrasound as their initial imaging are fundamentally different from those who are diagnosed after other imaging. Because patients undergoing ultrasound are younger and healthier and are diagnosed with lower-risk thyroid cancer, they are less likely to die of their thyroid cancer. However, being diagnosed with thyroid cancer can lead to cancer-related worry and create risks for harm from treatments. Thus, efforts are needed to reduce inappropriate use of ultrasound, abide by the U.S. Preventive Services Task Force recommendations, and apply nodule risk stratification tools when appropriate.