MON-545 Clinical Characteristics and Outcome of Clinically-Detected versus Imaging-Detected Incidental Thyroid Cancer

Introduction: Incidence and prevalence of thyroid cancer is increasing worldwide due to increased awareness of thyroid nodular diseases, advances in diagnostic tools and widespread use of imaging techniques. However, very few literatures reported the differences between clinically discovered and incidentally found thyroid cancer. Objective: The objective of this study was to evaluate clinical characteristics and outcome of clinically-detected and imaging-detected incidental thyroid cancer. Materials and Methods: This is a retrospective cohort study of 180 pathologically confirmed thyroid cancer patients who received thyroid surgery between January to December 2011 in Taipei Veterans General Hospital and had been long-term followed up with data on cancer outcome. Patients were categorized into two groups: group A (clinically-detected, n=127) and group B (imaging-detected incidental cancer, n=53). Results: In group A, the initial symptoms that prompted further investigation for thyroid disease included palpable mass (n=96), enlarged neck (n=11), change of voice (n=5), swallowing difficulty (n=7), breathing difficulty (n=6) and other non-specific discomfort (n=2). In group B, the initial image was ordered during health check-up in 30 patients and because of health issues other than thyroid disease in 23 patients. The imaging modalities included neck sonography (n=37), neck or chest computed tomography (n=5), whole body magnetic resonance imaging (n=9), whole body bone scan (n=1), positron emission tomography (n=1). Age, sex, tumor number, lobe involvement, AJCC staging, treatment modalities were not statistically different between the two groups. Mean tumor size was larger in group A (2.1±1.6 cm) compared to group B (1.2±0.9 cm, , P<0.001). Papillary thyroid microcarcinoma was more common in group B (26/53 = 49.0%) than group A (27/127 = 21.3%). No medullary or follicular thyroid carcinoma were detected in group B. Both groups contained mainly American Joint Committee on Cancer (AJCC) stage I disease (group A v.s. group B, 88/127 = 69.3% v.s. 40/53 = 75.5%). Recurrence free survival was not significantly different in the two groups (group A v.s. group B, 1177.7 v.s. 1247.5 days, P=0.14). In multivariate analysis, tumor size is still significantly different (group B v.s. group A, adjusted OR=0.56, P=0.001). Conclusion: Our result indicated that tumor size was significantly smaller in imaging-detected incidental thyroid cancer compared to clinical symptoms oriented ones. Although recurrence free survival was slightly longer in group B, the insignificant difference among the two groups does not encourage the wide-spread use of imaging techniques to detect smaller thyroid cancers.