Background: The incidence of well-differentiated thyroid cancer (WDTC) in the United States is increasing rapidly. Much of this increase is due to the detection by imaging of small, nonpalpable tumors. The incidence of advanced WDTC is also increasing, suggesting a true increase in the incidence of WDTC. This study was performed to determine how WDTCs of all sizes and stages are initially detected.
Methods: A retrospective chart review of 519 patients who underwent surgery for WDTC from January 1, 2007, through August 31, 2010, was performed. A total of 473 patients suitable for inclusion in this study were divided into three groups based upon the method by which the tumor was initially detected: tumors detected by an imaging study (184 patients-39%), those detected because a mass was felt in the neck (218 patients-46%), and those detected incidentally on pathological study of the surgical specimen (71 patients-15%). Method of detection was correlated with age and sex of the patient, and size, stage, and nodal status of the tumor.
Results: Patients in the Palpation group were more likely to be female (79% vs. 67% vs. 74%), younger (46 vs. 51 vs. 52), and to have larger tumors than those in the Imaging or Incidental groups. In the Imaging group, the tumor was detected on thyroid sonogram in 98 (53%), computed tomography in 38 (21%), magnetic resonance imaging in 19 (10%), carotid duplex scan in 14 (8%), and positron-emission tomography or other imaging studies in 15 (8%). Thirty-three percent of tumors <1 cm, 51% 1-2 cm, 29% 2-4 cm, and 38% >4 cm were first detected on an imaging study. Forty-seven percent of Stage III and IV cancers in patients aged ≥45 years and 39% of patients with positive central nodes were in the Imaging group.
Conclusion: This study demonstrates that while most tumors discovered by imaging were small and early stage, almost half of advanced (Stage III and IV) WDTCs were initially discovered by imaging studies. These findings are consistent with the hypothesis that the frequent use of imaging studies may explain not only the increasing incidence of early WDTC, but more advanced thyroid cancers as well.