Background: The association between Graves’ disease (GD) and co-existing thyroid cancer is still controversial and most of the previously reported data have been based on surgically treated GD patients. This study investigated the clinicopathological findings and prognosis of concomitant thyroid cancer in GD patients in the era of widespread application of ultrasonography. Methods: Data of GD patients who underwent thyroidectomy for thyroid cancer between 2010 and 2019 in three tertiary hospitals in South Korea (Asan Medical Center, Chonnam National University Hwasun Hospital, and Pusan National University Hospital) were collected and analyzed retrospectively. In the subgroup analysis, aggressiveness and clinical outcomes of thyroid cancer were compared nodular GD and non-nodular GD groups according to the presence or absence of the thyroid nodules other than thyroid cancer (index nodules). Results: Of the 15,159 GD patients treated at the hospitals during the study period, 262 (1.7%) underwent thyroidectomy for coexisting thyroid cancer. Eleven patients (4.2%) were diagnosed with occult thyroid cancer and 182 patients (69.5%) had microcarcinomas. No differences in thyroid cancer aggressiveness, ultrasonographic findings, or prognosis were observed between the nodular GD and non-nodular GD groups except the cancer subtype. In the multivariate analysis, only lymph node (LN) metastasis was an independent prognostic factor for recurrent/persistent disease of thyroid cancer arising in GD (P=0.020). Conclusion The prevalence of concomitant thyroid cancer in GD patients was considerably lower than in previous reports. The clinical outcomes of thyroid cancer in GD patients were also excellent but, more cautious follow-up is necessary for patients with LN metastasis in the same way as for thyroid cancer in non-GD patients.

Background: Hürthle cell carcinoma (HCC), a type of thyroid carcinoma, is rare in South Korea, and few studies have investigated its prognosis. Methods: This long-term multicenter retrospective cohort study evaluated the clinicopathological features and clinical outcomes in patients with HCC who underwent thyroid surgery between 1996 and 2009. Results: The mean age of the 97 patients included in the study was 50.3 years, and 26.8% were male. The mean size of the primary tumor was 3.2±1.8 cm, and three (3.1%) patients had distant metastasis at initial diagnosis. Ultrasonographic findings were available for 73 patients; the number of nodules with low-, intermediate-, and high suspicion was 28 (38.4%), 27 (37.0%), and 18 (24.7%), respectively, based on the Korean-Thyroid Imaging Reporting and Data System. Preoperatively, follicular neoplasm (FN) or suspicion for FN accounted for 65.2% of the cases according to the Bethesda category, and 13% had malignancy or suspicious for malignancy. During a median follow-up of 8.5 years, eight (8.2%) patients had persistent/recurrent disease, and none died of HCC. Older age, gross extrathyroidal extension (ETE), and widely invasive types of tumors were significantly associated with distant metastasis (all P<0.01). Gross ETE (hazard ratio [HR], 27.7; 95% confidence interval [CI], 2.2 to 346.4; P=0.01) and widely invasive classification (HR, 6.5; 95% CI, 1.1 to 39.4; P=0.04) were independent risk factors for poor disease-free survival (DFS). Conclusion The long-term prognosis of HCC is relatively favorable in South Korea from this study, although this is not a nation-wide data, and gross ETE and widely invasive cancer are significant prognostic factors for DFS. The diagnosis of HCC by ultrasonography and cytopathology remains challenging.

Radioiodine refractory differentiated thyroid cancers are rare but they make a definite problem since they run relentlessly progressive course leading to death in a few years. Recent development of various tyrosine kinase inhibitors significantly prolonged the overall survival of these patients. Currently available agents are mostly directed to VEGFR and are not specific to thyroid cancer and their efficacy is somewhat limited for a certain period of time. Very recently developed specific agents can significantly prolong the overall survival of these patients without serious adverse event and probably this kind of precision medicine shall be available to all the patients in near future but at present successive salvage treatment using different angiogenesis inhibitors may be an alternative option.

Purpose: The diagnostic performance of thyroid biopsy is influenced by several factors, including differences in the Bethesda categorization for malignancy, the inclusion or exclusion of non-diagnostic results, the definition used for the final diagnosis, and the definition of an inconclusive diagnosis. The purpose of this study was to provide an understanding of the factors influencing the diagnostic performance of thyroid biopsy. Methods: We collected data retrospectively between January and December 2013 from a cohort of 6,762 thyroid nodules from 6,493 consecutive patients who underwent biopsy. In total, 4,822 nodules from 4,553 patients were included. We calculated the biopsy sensitivity according to the inclusion of different Bethesda categories in the numerator and the exclusion of non-diagnostic results, as well as the diagnostic accuracy according to different definitions of a benign diagnosis. We obtained the conclusive and inconclusive diagnosis rates. Results: The sensitivity increased when more Bethesda categories were included in the numerator and when non-diagnostic results were excluded. When a benign thyroid nodule diagnosis was defined as benign findings on surgical resection, concordant benign results on at least two occasions, or an initial benign biopsy result and follow-up for more than 12 months, the accuracy was higher than when the diagnosis was based on surgical resection alone (68.7% vs. 91.1%). A higher conclusive diagnosis rate was obtained (78.3% vs. 72.8%, P<0.001) when Bethesda categories I and III were considered inconclusive. Conclusion Understanding the concepts presented herein is important in order to appropriately interpret the diagnostic performance of thyroid biopsy.

Background: Serum calcitonin measurement contains various clinical and methodological aspects. Its reference level is wide and unclear despite sensitive calcitonin kits are available. This study aimed to identify the specific reference range in the healthy Korean adults. Methods: Subjects were ≥20 years with available calcitonin (measured by a two-site immunoradiometric assay) data by a routine health checkup. Three groups were defined as all eligible subjects (group 1, n=10,566); subjects without self or family history of thyroid disease (group 2, n=5,152); and subjects without chronic kidney disease, autoimmune thyroid disease, medication of proton pump inhibitor/H2 blocker/steroid, or other malignancies (group 3, n=4,638). Results: This study included 6,341 male and 4,225 female subjects. Males had higher mean calcitonin than females (2.3 pg/mL vs. 1.9 pg/mL, P<0.001) in group 1. This gender difference remained similar in groups 2 and 3. Calcitonin according to age or body mass index was not significant in both genders. Higher calcitonin in smoking than nonsmoking men was observed but not in women. Sixty-nine subjects had calcitonin higher than the upper reference limit (10 pg/mL) and 64 of them had factors associated with hypercalcitoninemia besides medullary thyroid cancer. Our study suggests the reference intervals for men who were non, ex-, current smokers, and women (irrespective of smoking status) as <5.7, <7.1, <7.9, and <3.6 pg/mL, respectively. Conclusion Specific calcitonin reference range should be provided considering for sex and smoking status. Taking account for several factors known to induce hypercalcitoninemia can help interpret the gray zone of moderately elevated calcitonin.

Active surveillance (AS) for low-risk papillary thyroid microcarcinoma (PTMC) has been accepted worldwide as safe and effective. Despite the growing acceptance of AS in the management of low-risk PTMCs, there are barriers to AS in real clinical settings, and it is important to understand and establish appropriate AS protocol from initial evaluation to follow-up. PTMC management strategies should be decided upon after careful consideration of patient and tumor characteristics by a multidisciplinary team of thyroid cancer specialists. Patients should understand the risks and benefits of AS, participate in decision-making and follow structured monitoring strategies. In this review, we discuss clinical outcomes of AS from previous studies, optimal indications and follow-up strategies for AS, and unresolved questions about AS.

Background: Serum calcitonin measurement contains various clinical and methodological aspects. Its reference level is wide and unclear despite sensitive calcitonin kits are available. This study aimed to identify the specific reference range in the healthy Korean adults. Methods: Subjects were ≥20 years with available calcitonin (measured by a two-site immunoradiometric assay) data by a routine health checkup. Three groups were defined as all eligible subjects (group 1, n=10,566); subjects without self or family history of thyroid disease (group 2, n=5,152); and subjects without chronic kidney disease, autoimmune thyroid disease, medication of proton pump inhibitor/H2 blocker/steroid, or other malignancies (group 3, n=4,638). Results: This study included 6,341 male and 4,225 female subjects. Males had higher mean calcitonin than females (2.3 pg/mL vs. 1.9 pg/mL, P<0.001) in group 1. This gender difference remained similar in groups 2 and 3. Calcitonin according to age or body mass index was not significant in both genders. Higher calcitonin in smoking than nonsmoking men was observed but not in women. Sixty-nine subjects had calcitonin higher than the upper reference limit (10 pg/mL) and 64 of them had factors associated with hypercalcitoninemia besides medullary thyroid cancer. Our study suggests the reference intervals for men who were non, ex-, current smokers, and women (irrespective of smoking status) as <5.7, <7.1, <7.9, and <3.6 pg/mL, respectively. Conclusion Specific calcitonin reference range should be provided considering for sex and smoking status. Taking account for several factors known to induce hypercalcitoninemia can help interpret the gray zone of moderately elevated calcitonin.

Active surveillance (AS) for low-risk papillary thyroid microcarcinoma (PTMC) has been accepted worldwide as safe and effective. Despite the growing acceptance of AS in the management of low-risk PTMCs, there are barriers to AS in real clinical settings, and it is important to understand and establish appropriate AS protocol from initial evaluation to follow-up. PTMC management strategies should be decided upon after careful consideration of patient and tumor characteristics by a multidisciplinary team of thyroid cancer specialists. Patients should understand the risks and benefits of AS, participate in decision-making and follow structured monitoring strategies. In this review, we discuss clinical outcomes of AS from previous studies, optimal indications and follow-up strategies for AS, and unresolved questions about AS.

Background/Aims: To evaluate the association between the urinary sodium concentration and iodine status in different age groups in Korea. Methods: This nationwide, population-based, cross-sectional study used data from the Korean National Health and Nutrition Examination Survey (VI 2-3, 2014 to 2015). We included 3,645 subjects aged 10 to 75 years with normal kidney function and without a history of thyroid disease. Adequate iodine intake was defined as a urinary iodine/creatinine (I/Cr) ratio of 85 to 220 µg/g. The urinary sodium/ creatinine (Na/Cr) ratios were classified as low (< 47 mmol/g), intermediate (47 to 114 mmol/g), or high (> 114 mmol/g). Results: The median urinary iodine concentration (UIC) was 292 µg/L (interquartile range [IQR], 157 to 672), and the median urinary I/Cr ratio was 195 µg/g (IQR, 104 to 478). Iodine deficiency (< 100 µg/L) and iodine excess (> 300 µg/L) were observed in 11.3% and 49.0% of subjects, respectively. The UIC was significantly associated with the urinary sodium concentration, and the urinary I/Cr ratio was significantly correlated with the urinary Na/Cr ratio (both p < 0.001). The distributions of UIC, urinary I/Cr ratio, and Na/Cr ratio varied among age groups. Low urinary I/Cr and Na/Cr ratios were most common in young adults (age, 19 to 29 years), while high urinary I/Cr and Na/Cr ratios were most common in elderly people (age, 60 to 75 years). Conclusions Iodine intake was significantly associated with sodium intake in the Korean population. Our study suggested that an adequately low salt intake might be helpful for preventing iodine excess in Korea.