Abstract：
This review summarizes the changes in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors that relate to the thyroid gland. The new classification has divided thyroid tumors into several new categories that allow for a clearer understanding of the cell of origin, pathologic features (cytopathology and histopathology), molecular classification, and biological behavior. Follicular cell-derived tumors constitute the majority of thyroid neoplasms. In this new classification, they are divided into benign, low-risk, and malignant neoplasms. Benign tumors include not only follicular adenoma but also variants of adenoma that are of diagnostic and clinical significance, including the ones with papillary architecture, which are often hyperfunctional and oncocytic adenomas. For the first time, there is a detailed account of the multifocal hyperplastic/neoplastic lesions that commonly occur in the clinical setting of multinodular goiter; the term thyroid follicular nodular disease (FND) achieved consensus as the best to describe this enigmatic entity. Low-risk follicular cell-derived neoplasms include non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), thyroid tumors of uncertain malignant potential, and hyalinizing trabecular tumor. Malignant follicular cell-derived neoplasms are stratified based on molecular profiles and aggressiveness. Papillary thyroid carcinomas (PTCs), with many morphological subtypes, represent the BRAF-like malignancies, whereas invasive encapsulated follicular variant PTC and follicular thyroid carcinoma represent the RAS-like malignancies. This new classification requires detailed subtyping of papillary microcarcinomas similar to their counterparts that exceed 1.0 cm and recommends not designating them as a subtype of PTC. The criteria of the tall cell subtype of PTC have been revisited. Cribriform-morular thyroid carcinoma is no longer classified as a subtype of PTC. The term \"Hürthle cell\" is discouraged, since it is a misnomer. Oncocytic carcinoma is discussed as a distinct entity with the clear recognition that it refers to oncocytic follicular cell-derived neoplasms (composed of > 75% oncocytic cells) that lack characteristic nuclear features of PTC (those would be oncocytic PTCs) and high-grade features (necrosis and ≥ 5 mitoses per 2 mm2). High-grade follicular cell-derived malignancies now include both the traditional poorly differentiated carcinoma as well as high-grade differentiated thyroid carcinomas, since both are characterized by increased mitotic activity and tumor necrosis without anaplastic histology and clinically behave in a similar manner. Anaplastic thyroid carcinoma remains the most undifferentiated form; squamous cell carcinoma of the thyroid is now considered as a subtype of anaplastic carcinoma. Medullary thyroid carcinomas derived from thyroid C cells retain their distinct section, and there is a separate section for mixed tumors composed of both C cells and any follicular cell-derived malignancy. A grading system for medullary thyroid carcinomas is also introduced based on mitotic count, tumor necrosis, and Ki67 labeling index. A number of unusual neoplasms that occur in the thyroid have been placed into new sections based on their cytogenesis. Mucoepidermoid carcinoma and secretory carcinoma of the salivary gland type are now included in one section classified as \"salivary gland-type carcinomas of the thyroid.\" Thymomas, thymic carcinomas and spindle epithelial tumor with thymus-like elements are classified as \"thymic tumors within the thyroid.\" There remain several tumors whose cell lineage is unclear, and they are listed as such; these include sclerosing mucoepidermoid carcinoma with eosinophilia and cribriform-morular thyroid carcinoma. Another important addition is thyroblastoma, an unusual embryonal tumor associated with DICER1 mutations. As in all the WHO books in the 5th edition, mesenchymal and stromal tumors, hematolymphoid neoplasms, germ cell tumors, and metastatic malignancies are discussed separately. The current classification also emphasizes the value of biomarkers that may aid diagnosis and provide prognostic information.
摘要：
这篇综述总结了第5版WHO内分泌和神经内分泌肿瘤分类中与甲状腺有关的变化。新的分类将甲状腺肿瘤分为几个新的类别，可以更清楚地了解起源的细胞，病理特征（细胞病理学和组织病理学），分子分类，和生物学行为。滤泡细胞源性肿瘤占甲状腺肿瘤的大多数。在这个新的分类中，它们分为良性，低风险,和恶性肿瘤。良性肿瘤不仅包括滤泡性腺瘤，还包括具有诊断和临床意义的腺瘤变体。包括有乳头状结构的，通常是功能亢进和嗜酸细胞腺瘤。第一次,多结节性甲状腺肿临床中常见的多灶性增生/肿瘤性病变有详细的描述;术语甲状腺滤泡性结节性疾病(FND)获得共识,是描述这一神秘实体的最佳方法.低危滤泡细胞源性肿瘤包括具有乳头状样细胞核特征（NIFTP）的非侵袭性滤泡性甲状腺肿瘤，不确定恶性潜能的甲状腺肿瘤，和透明质化小梁肿瘤。恶性滤泡细胞衍生的肿瘤根据分子谱和侵袭性进行分层。甲状腺乳头状癌，有许多形态亚型，代表BRAF样恶性肿瘤，而浸润性包囊滤泡型变异型PTC和滤泡型甲状腺癌代表RAS样恶性肿瘤。这种新分类要求对乳头状微癌进行详细的分型，类似于超过1.0厘米的乳头状微癌，建议不要将其指定为PTC的亚型。已经重新审视了PTC的高细胞亚型的标准。结节性甲状腺癌不再被归类为PTC的亚型。不鼓励使用术语“Hürthle单元格”，因为这是一个误称。讨论了嗜酸细胞癌是一种独特的实体，明确认识到它是指缺乏PTC（那些将是嗜酸细胞PTC）的特征性核特征的嗜酸细胞滤泡细胞衍生的肿瘤（由>75％的嗜酸细胞组成）和高级特征（每2mm2坏死和≥5个有丝分裂）。现在，高级别滤泡细胞衍生的恶性肿瘤包括传统的低分化癌和高级别分化甲状腺癌，因为两者都以有丝分裂活性增加和肿瘤坏死为特征，没有间变性组织学和临床表现相似。间变性甲状腺癌仍然是最未分化的形式；甲状腺鳞状细胞癌现在被认为是间变性癌的一种亚型。源自甲状腺C细胞的甲状腺髓样癌保留其独特的切片，并且有一个由C细胞和任何滤泡细胞衍生的恶性肿瘤组成的混合肿瘤的单独部分。还引入了基于有丝分裂计数的甲状腺髓样癌分级系统，肿瘤坏死,和Ki67标签索引。甲状腺中发生的许多不寻常的肿瘤已根据其细胞发生而被置于新的切片中。唾液腺型粘液表皮样癌和分泌性癌现在被列入一个分类为“唾液腺型甲状腺癌”的部分。\"胸腺瘤,胸腺癌和具有胸腺样元素的梭形上皮肿瘤被归类为甲状腺内的胸腺肿瘤。“仍有几种肿瘤的细胞谱系尚不清楚，它们被列为此类；这些包括伴有嗜酸性粒细胞增多的硬化性黏液表皮样癌和筛状-乳头状甲状腺癌。另一个重要的补充是甲状腺母细胞瘤，与DICER1突变相关的异常胚胎性肿瘤。就像世界卫生组织第5版的所有书籍一样，间充质和间质肿瘤，血淋巴样肿瘤，生殖细胞肿瘤,和转移性恶性肿瘤分开讨论。目前的分类还强调了可能有助于诊断和提供预后信息的生物标志物的价值。
