Thyroid FNA cytology in Asian practice—Active surveillance for indeterminate thyroid nodules reduces overtreatment of thyroid carcinomas

Abstract

Although Asian thyroid practices have implemented the American Thyroid Association guidelines, significant deviations in actual risk of malignancy (ROM) have been reported. With review of the literature from Asia, the authors examine the underlining reasons for actual ROMs reported in Asia being so different from western practice based on the author's perspective. Although the most popular diagnostic system for thyroid cytology used in Asian countries is the Bethesda system, the Japan Thyroid Association published clinical guidelines, including a national reporting system for thyroid cytology, to adapt conservative clinical management (active surveillance and strict triage patients for surgery) for low-risk thyroid carcinomas. As less aggressive clinical management is favoured in Asian societies, strict triage of patients with indeterminate thyroid nodules for surgery is usually applied, which ultimately reduces overtreatment of indolent thyroid tumours. As a result, low resection rates and high ROMs for indeterminate nodules were achieved in Asian practices using the same Bethesda system. Recently, borderline thyroid tumours were introduced in the thyroid tumour classification and significant decreases in ROMs have been reported in the indeterminate categories in western practice.However, ROM of indeterminate nodules remained high in Asian practice even after borderline tumours were deemed benign. These results suggested that the diagnostic threshold of papillary thyroid carcinoma-type nuclear features varied among practices (stricter in Asia than in western practice), and diagnostic surgery was not performed for a significant number of indeterminate nodules with benign clinical features in Asian practice, resulting in low rates of borderline tumours in surgicallytreated patients. K E Y W O R D SAsia, borderline tumour, indeterminate cytology, resection rate, risk of malignancy, thyroid FNAC

Web‐based thyroid imaging reporting and data system: Malignancy risk of atypia of undetermined significance or follicular lesion of undetermined significance thyroid nodules calculated by a combination of ultrasonography features and biopsy results

“…This web-based scoring system could be used in daily practice to calculate and estimate the risk of malignancy of thyroid nodules on the basis of ultrasound findings and biopsy results. 34 Hong et al 35 suggested repeat biopsy or surgery for AUS/FLUS nodules with intermediate or high suspicion on ultrasound patterns (Korean TIRADS 4 or 5) and a malignant risk ranging from 30%-90%. The areas under the receiver operating characteristic (ROC) curves were 0.837 and 0.773 for the new and old prediction models, respectively nodules according to ultrasound findings, as well as several TIRADS and risk-stratification systems, were all developed for use in thyroid nodule risk stratification using various ultrasound features.…”

The new 4th edition World Health Organization classification for thyroid tumors, Asian perspectives

“…This is because there are significant and irreconcilable differences between Asian and Western practices for management of thyroid nodules and thyroid cancer. These differences include the following: (i) Asian patient populations live in mostly iodine sufficient countries and the histological type of the majority of thyroid carcinoma is papillary thyroid carcinoma (PTC); (ii) the prevalence of the BRAF V600E point mutation in Asian PTC cohorts is higher than that reported from Western countries; (iii) it is well‐known that significant numbers of patients with low‐risk papillary microcarcinoma (PMC) are treated conservatively (active surveillance) in Asia instead of by immediate surgery; (iv) resection of indeterminate thyroid nodules is quickly selected in Western practice and diagnostic surgery is more common to prevent missing malignancy due to medicolegal reasons in Western practice; and (v) approaches for low‐risk thyroid carcinoma (lobectomy instead of total thyroidectomy) are more conservative in Asia . Therefore, many important publications from Asia were not well acknowledged in the WHO classification or in most Western clinical guidelines, as those data obtained from Asian practice are not reproducible in current Western practice .…”

“…Even if they are found to be malignant tumors and adverse events develop, they can be managed curatively as long as they are encapsulated and intrathyroidal tumors (ex0, N0 and M0). In our Asian and Australasian experience, the vast majority of borderline tumors are diagnosed in the benign category (FA), and clinically significant cancers are rarely missed using this conservative approach . However, some intrathyroidal tumors are true malignant tumors and have a non‐negligible risk for structural disease recurrence, such as non‐encapsulated 2‐4 cm PTC (5% of recurrence) and BRAF mutated <4 cm PTC (10% of recurrence), but they can be detected preoperatively by applying a multidisciplinary clinical approach by experienced clinicians and pathologists …”

“…classified PTC into low risk and high risk groups for disease recurrence based on features of so‐called aggressive histology (tall/columnar cell, micropapillary/discohesive and solid variant PTC) in 2008, and some other Japanese studies risk‐stratified follicular cell thyroid carcinomas into three groups (low‐risk, moderate‐risk and high‐risk) using clinical features, the Ki67 proliferation index and thyroglobulin doubling time . In 2009, the previous ATA clinical guidelines recommended risk stratification of differentiated thyroid carcinomas into low‐risk, intermediate‐risk and high‐risk for structural disease recurrence using a combination of histopathological parameters and clinical features, and was updated in 2016 (Table ) to guide management and determine the need for radioactive iodine ablation therapy, so‐called risk adapted management . The histopathological parameters used for risk stratification were the presence of (i) aggressive histology (diffuse sclerosing, tall cell, columnar cell, hobnail and solid variant PTC), (ii) minor (microscopic) and gross extrathyroidal extension, (iii) more than four or fewer than four foci of vascular invasion, (iv) extranodal invasion, (v) fewer than five involved lymph nodes (less than 0.2 cm metastasis), (vi) more than five involved lymph nodes (0.2–3 cm), and (vii) intrathyroidal (ex0, N0, M0) differentiated thyroid carcinomas (Table ).…”

Diagnostic value of HBME‐1, CK19, Galectin 3, and CD56 in the subtypes of follicular variant of papillary thyroid carcinoma

“…This re‐classification provided evidence for limited operation (i.e., lobectomy without lymph node dissection) for NIFTP cases. Furthermore, the Japan Thyroid Association recommended active surveillance without diagnostic surgery for indeterminate thyroid nodules including NIFTP …”