Beyond genetic and biological differences, cultural practices and socio-environmental determinants in Asia can greatly influence thyroid pathology outcomes. For instance, dietary iodine intake, prevalent in many Asian diets, can significantly affect thyroid physiology and pathology.

Diverse Asian nations, with their distinct historical trajectories, have developed unique healthcare infrastructures. The accessibility and quality of healthcare, including diagnostic facilities, can vary even within countries, let alone between them.

The juxtaposition of North American and Asian healthcare expenditure strategies underlines more profound socio-economic and policy-driven differences. These variations often dictate clinical decisions, with patient affordability playing a crucial role. Medical expenses vary significantly across countries, with North America typically experiencing higher costs. Immediate surgery is frequently chosen to reduce these expenses. However, in other parts of the world, the approach often leans towards risk stratification for surgery and long-term clinical monitoring, as these tend to be more cost-effective than surgical interventions compared to the United States.

Health insurance schemes’ dynamics, influenced by public policies and private market forces, can significantly sway diagnostic and treatment choices.

The density of pathologists across countries significantly shapes the landscape of medical practice [17]. The number of pathologists in a country is intrinsically linked to the efficiency and effectiveness of its medical system.

The medico-legal environment molds clinical practice considerably. In some countries, clinical practice guidelines are established with a defensive approach due to the potential for physicians to face malpractice lawsuits. While defensive medicine may seem prudent in litigious societies, it can inadvertently lead to overdiagnosis and overtreatment, escalating healthcare costs. Conversely, other nations resist such defensive medicine because it escalates societal costs and burdens patients financially [18-20].

The evolution of medical terminologies and classifications, often reflecting deeper understandings of diseases, underscores the importance of constant knowledge exchange and adaptation among global medical communities. The noninvasive encapsulated follicular variant of papillary thyroid carcinoma (FVPTC) was once classified as a malignant tumor in American thyroid nodule practices. Its prevalence in the West is elevated due to a lower threshold for recognizing papillary thyroid carcinoma (PTC) nuclear features (Fig. 1) [21,22]. However, this classification was later changed to noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) [2,23]. In many Asian practices, these are typically observed in benign follicular adenomas (FAs) due to a higher threshold for PTC-type nuclear features (Fig. 1), resulting in a lower prevalence of NIFTP in surgically removed nodules in Asia [2,8,11,12,14-16].

The decision-making algorithms in medicine are based on clinical evidence, patient preferences, physician experiences, and systemic constraints. In Asian clinical practice, a more conservative management approach is typically adopted, emphasizing clinical risk stratification for high-risk indeterminate thyroid nodules, specifically follicular neoplasm (FN) [9-11,13-16]. Conversely, in North America, diagnostic surgery becomes the preferred course when patients cannot afford molecular tests [1,4,9, 10,11,13-15]. Consequently, in the West, indeterminate nodules, categorized as Bethesda III (atypia of undetermined significance [AUS]) and IV (FN), have a high resection rate (RR) of over 50% but a lower risk of malignancy (ROM) of less than 30%. In contrast, most Asian practices show a lower RR of less than 40% for these nodules, with a ROM exceeding 40%, even in the absence of molecular testing [9-11,13-16].

Each country, influenced by its unique medical history, patient demographics, and healthcare policies, carves out its distinct approach to disease management. In Japan, a more conservative approach to management is prevalent [10,11,24-26]. Traditionally, lobectomy is the chosen procedure for low-risk small PTCs measuring 1–2 cm and for slightly larger low-risk PTCs, specifically, those sized less than 4 cm and categorized as T1–2, extrathyroidal extension (Ex) 0–1, N0–1, and M0 [24-26]. This conservative strategy offers notable benefits, most crucially the potential preservation of thyroid function. Such a conservative approach is particularly vital as patients who undergo total thyroidectomy and subsequently experience poorly managed hypothyroidism face severe risks, especially as they age and potentially struggle with proper hormone supplement management. Contrarily, in most other regions of Asia, as well as in North America and Europe, the predominant choice leans towards total thyroidectomy in the past [4,24-27].

The balance between surgical intervention and observation hinges on the collective experiences of a medical community, patient trust, and the broader healthcare framework. In Japan, over half of the patients with low-risk, small PTCs (less than 10 mm) opt for active surveillance, undergoing clinical follow-ups without surgery once a fine needle aspiration (FNA) confirms the malignancy [4,28-31]. Conversely, in the majority of other nations, FNA is typically not recommended for thyroid nodules that are small and low-risk, especially those under 1 cm [4]. This distinction arises from the fact that once an FNA identifies a nodule as malignant, surgery becomes the frequent choice, leading to potential overtreatment for patients with low-risk, small PTCs [4,14-16].

As medicine advances, so does the need for precision. Nevertheless, precision must be juxtaposed against practicality in the light of resource optimization. Grossing techniques for encapsulated follicular pattern thyroid tumors vary globally. In Western countries, where pathologists often adopt defensive medical practices due to malpractice concerns, there is an emphasis on meticulously sampling the entire tumor capsules [2,15,16,32,33]. As recommended in Western textbooks, this practice has influenced the protocols in certain Asian laboratories, notably in China, Korea, Taiwan, and Thailand [32]. Conversely, Indian, Indonesian and Japanese labs generally select only representative sections, typically fewer than 10 per nodule, adhering to prior textbook guidelines [33,34]. This streamlined approach reduces the number of hematoxylin and eosin sections taken (from more than 20 sections to fewer than 10 per nodule) and conserves both pathologist time and societal resources.

The reasoning behind this more economical approach in India, Indonesia and Japan is multifaceted: (1) Lobectomy is deemed suitable for a range of nodules, from benign (e.g., FA) to borderline tumors (e.g., NIFTP, thyroid tumors of uncertain malignant potential), and even low-risk malignancies (like minimally invasive follicular thyroid carcinoma [FTC] or encapsulated conventional PTC) [4,24-26,33]. (2) Only pronounced, clear invasions carry significant implications for a patient’s prognosis. With this method focused on Sustainable Development Goals, there is virtually no risk of overlooking clinically consequential carcinomas, such as extensively angio-invasive or widely invasive carcinomas [2,3,33]. (3) Conducting exhaustive histological examinations to identify ambiguous invasions can result in the overtreatment of low-risk tumors, such as those termed minimally invasive FTCs or encapsulated FVPTCs (EFVPTCs). (4) Restricting the number of samples (to less than 10 sections) mirrors the clinical guideline of refraining from FNAs on low-risk thyroid nodules smaller than 1 cm. This approach encourages a clinical follow-up, subsequently reducing surgeries for small papillary carcinomas. Moreover, limiting samples can mitigate the unintended identification of questionable capsular invasions and, consequently, the diagnoses of minimally invasive FTCs and EFVPTCs. This, in turn, lessens the likelihood of excessive treatments, like completion thyroidectomy or radioactive iodine abrasion, particularly for very low-risk thyroid tumors with negligible prognostic impact [36-39].

How we classify and interpret diagnostic samples evolves with our understanding of disease processes and the nuances of clinical implications. In past cytological practices, including in the United States, cyst fluid only samples from thyroid FNA cytology were typically categorized as benign. However, current Western practices have moved these samples to the inadequate category due to the substantial risk they pose for false-negative diagnoses and the potential inability to completely exclude cystic PTC [1,14-16]. In contrast, some countries in Asia/Oceania still classify these samples as benign, while European countries might place them in a specific subcategory under the inadequate category. This reclassification in Europe is attributed to the extremely low malignancy risk associated with these samples, which is on par with or even lower than the risk associated with samples in the benign category [9,15,16].

A noninvasive encapsulated follicular pattern tumor, which exhibited worrisome nuclear features characteristic of PTC (RAS-like dysplasia), was previously categorized as a malignant tumor (FVPTC). This classification was predominant due to the lower threshold set for malignancy based on RAS-like PTC nuclear features in earlier Western thyroid nodule practices [5-8,21-23, 40-45]. This classification was later revised to “NIFTP” and was categorized as a borderline tumor in the 4th edition of the WHO classification [2,23,42,43]. Comprehensive data regarding the global incidence of NIFTP was derived from a thorough review of published studies and collaborative research efforts by members of the Asian Thyroid Working Group. These studies ascertained that the global occurrence of NIFTP is notably less than what was initially anticipated [12,47,48]. Furthermore, the incidence rates of NIFTP in Asia are substantially lower than those observed in North American and European regions. This discrepancy stems from the perception of NIFTP in Asia—it isn’t deemed to necessitate surgical intervention. Instead, a conservative approach that emphasizes risk stratification for surgical interventions is the conventional clinical protocol for managing indeterminate thyroid nodules in Asia [9-11,14-16]. This practice is also influenced by the stringent criteria for identifying PTC-type nuclear features in the region (Fig. 1) [5,6,11,14-16,21,22,40].

This study analyzed 153 cases of primary thyroid lymphoma (PTL) collected from 10 institutions represented by members of the Asian Thyroid Working Group. The reported prevalence was 0.54% of all malignant thyroid tumors. The breakdown indicated that mucosa-associated lymphoid tissue lymphoma accounted for 54.9%, while diffuse large B-cell lymphoma represented 38.6%. Ultrasound examination and FNA cytology were the primary preoperative diagnostic tools, with flow cytometry conducted in five institutions. The findings suggest that the prevalence of PTL in non-Western countries is lower than previously reported in other studies.

Of 42,190 thyroid aspirates, 760 (1.8%) exhibited a predominance of Hürthle cells. These samples were sourced from nine hospitals across six Asian countries. The majority, or 61%, were categorized as “atypia of undetermined significance, Hürthle cell type” (AUS-H); 35% were identified as “follicular neoplasm, Hürthle cell type” (FN-H); and 4% were classified as “suspicious for malignancy” (SFM). Histologic follow-up was conducted for 288 of these aspirates (equivalent to 38%). Of these, a significant majority (66%) were determined to be benign upon resection, with the most common histologic diagnosis being Hürthle cell adenoma at 28.5%. The ROM for AUS-H, FN-H, and SFM, based on the resected nodules, was 32%, 31%, and 71%, respectively. Meanwhile, the risk of neoplasm was calculated to be 47%, 81%, and 77% for the respective categories.

From 13 hospitals across 8 Asia-Pacific countries, 145 cases of medullary (C cell) thyroid carcinoma (MTC) with accessible FNA slides were gathered for this study. Of these cases, 99 (68.3%) were preliminarily interpreted as either suspicious for MTC (SMTC) or confirmed as MTC. While cytological detection alone for MTC showed limitations, the combined application with auxiliary tests substantially enhanced diagnostic proficiency. The staining techniques employed varied across institutions and included Papanicolaou, hematoxylin-eosin, and Romanowsky methods. Liquid-based cytology was implemented in merely three of the countries. Following a comprehensive review of all cases, the diagnostic rate for MTC or S-MTC rose to 91.7% (133 out of the 145 cases). Based solely on cytomorphologic data, a plausible scoring system has been suggested to ensure optimal diagnostic precision. Additionally, Jung et al. [57] provided an overview of the latest advancements and modifications related to MTC as delineated in the WHO classification.

This investigation assessed interobserver concordance in evaluating capsular invasion among 11 thyroid pathologists from five Asian countries. This was accomplished using 20 cases presented as virtual slides. The levels of agreement for definitive invasive and noninvasive classifications were fair, evidenced by kappa values of 0.578 and 0.404, respectively. However, concordance was poor for cases with ambiguous invasion, as indicated by a kappa value of 0.186. The discrepancies in invasion assessment led to divergent final pathological conclusions. In summary, the research highlighted significant interobserver variability in the assessment of capsular invasion, particularly in FNs where the invasion was debatable.

This study examined whether pathologists could distinguish BRAF-like and RAS-like nuclear features morphologically. This analysis suggests that nuclear pseudo-inclusions and high nuclear scores have diagnostic utility as rule-in markers for differentiating PTC with BRAF V600E mutation from benign or borderline follicular tumors with RAS-like mutations. Relaxation of rigid criteria for nuclear features resulted in an overdiagnosis of PTC. Immunostaining or molecular testing for BRAF V600E mutation is a valuable adjunct for cases with high nuclear scores to identify true PTC.

The term “noninvasive encapsulated papillary RAS-like thyroid tumor (NEPRAS)” was introduced by Ohba et al. in 2019 [61] to describe a noninvasive thyroid tumor characterized by a complete fibrous capsule, a predominantly papillary architecture, and the presence of a RAS mutation, yet exhibiting only subtle nuclear features consistent with PTC (RAS-like dysplasia). This tumor poses a challenge for pathologists as it lies at the intersection between an encapsulated conventional BRAF-like PTC and the FA with papillary architecture, which was recognized as a benign tumor entity in the 5th edition of the WHO classification [2,3].

To address the diagnostic challenge and reduce the psychological impact on patients, the term “NEPRAS” was proposed, echoing the approach taken with the NIFTP terminology as introduced by Nikiforov et al. [23]. Subsequently, Jung et al. [62] documented three additional cases, suggesting that a favorable prognosis could be anticipated following surgical resection of such tumors. This optimism is grounded in the understanding that most encapsulated thyroid tumors, when not invasive, tend to be indolent, mirroring the behavior of FAs regardless of their growth patterns (be it NIFTP in follicular or NEPRAS in papillary patterns) [37,38,63]. However, it is noteworthy that extensive long-term follow-up data on a large patient cohort still needs to be available [62].

TBSRTC outputs, including frequency and ROM for most categories, were not statistically different from data in adult patients. However, the RR in the pediatric group was significantly higher in most of the categories compared with published adult data: benign, 23.2% vs. 13.0%; AUS, 62.6% vs. 36.2%; FN, 84.3% vs. 60.5%; and SFM, 93.8% vs. 69.7%. Pediatric patients with benign and indeterminate thyroid nodules had a higher RR than their adult counterparts, but the ROM of these categories in adults and children was not statistically different, suggesting a potential risk of overtreatment in pediatric patients. Determining the best treatment guidelines and additional tools for risk stratification must be a top priority to identify the target patient groups for surgical intervention precisely. Our study further demonstrated that Asian pediatric thyroid nodules had higher ROM than those from adults.

This study examined the impact of coronavirus disease 2019 (COVID-19) on cytology practice in the Asia-Pacific region involving 167 cytopathology laboratories from 24 countries. The majority reported that restrictive measures that limited the accessibility of health care services had been implemented in their cities and/or countries (80.8%) and their hospitals (83.8%). Approximately one-half of the participants reported the implementation of new biosafety protocols (54.5%) and improving laboratory facilities (47.3%). The majority of the respondents reported a significant reduction (> 10%) in caseload associated with both gynecological (82.0%) and nongynecological specimens (78.4%). Ten out of 14 authors were from the Asian Thyroid Working Group members.

One of the most promising and valuable projects for pathologists is revising thyroid tumor classification, such as refining new tumor entities and establishing a molecular classification of thyroid tumors. The current WHO classification is insufficient for genuine molecular classification, and Western pathologists distinguish RAS-mutated encapsulated follicular pattern thyroid tumors into two tumor groups, FA/tumors of uncertain malignant potential (UMP)/FTC and NIFTP/UMP/FVPTC, according to the absence (NS 0–1) or presence (NS 2–3) of RAS-like dysplastic nuclear features (Fig. 1). This distinction has very little clinical imprecation because both are treated similarly, and the outcomes are almost identical [2,4]. In Asian thyroid practice, the distinction between FA/UMP/FTC and NIFTP/UMP/FVPTC is not strict and often handles them into one tumor lineage, FA/FTC. Thus, NIFTP and FVPTC are rare in Asia [12], while FTC is a vanishing tumor entity and is frequently classified as FVPTC in recent Western practice [75,76]. The lack of uniformity in diagnosing encapsulated follicular pattern tumors with delicate RAS-nuclear features among pathologists creates serious confusion in referring clinicians in some instances and hinders data sharing among institutes. It is a time to combine both RAS-like tumors into one tumor entity, as there are no benefits in the strict sub-classification of RAS-like tumors (FA/UMP/FTC vs. NIFTP/UMP/FVPTC) for treating physicians and patients. The author believes that universally accepted handling of the same RAS oncogene-mutated thyroid tumors is essential to minimize observer variation of encapsulated follicular pattern tumors and establish better communication between Asia and the West, harmonizing them into one world.

In 2016, a pivotal moment in pathology occurred with Nikiforov’s publication of a seminal paper introducing the borderline tumor entity known as NIFTP [23]. Recognizing the importance and potential implications of this new classification, Dr. Kakudo, in the same year, invited a distinguished cohort of 15 international authors, inclusive of four members from the Asian Thyroid Working Group, to present their perspectives and insights on NIFTP in the Journal of Basic & Clinical Medicine (Table 1). It is unfortunate that the journal above subsequently ceased its operations, and its digital presence has vanished. Nevertheless, most of the seminal works, including those discussing NIFTP, are retrievable online, specifically at Dr. Kakudo’s website (http://www.kakudok.jp/english/basic_and_ clinical_medicine/) and the individual ResearchGate profiles of the respective authors.

In the AOTA Busan meeting, the Asian Thyroid Working Group commenced its operations in 2017. To begin their collaborative efforts, the Asian Thyroid Working Group summarized and reported the prevailing status of thyroid FNA cytology practices across seven Asian nations. These findings were subsequently published in a special issue of the Journal of Pathology and Translational Medicine, sponsored by the Korean Society of Pathologists and the Korean Society for Cytopathology. The articles from this special issue are delineated below in Table 2.

“Asian and Western Practice in Thyroid Pathology: Similarities and Differences” was a themed issue published in Gland Surgery (Table 3). It addressed critical differences observed when Western systems for thyroid pathology and cytology were adopted in Asian practice. Dr. Kakudo invited 25 international authors, of which 19 are members of the Asian Thyroid Working Group. These original articles, reviews, and meta-analyses highlight significant differences. Some of these disparities are entirely understandable and expected, while others are deemed scientifically unacceptable and not suitable for patient-centered care.