Department of Pathology, Emory University Hospital Midtown, 550 Peachtree St. NE, Davis-Fischer Building Suite 1314-A, Atlanta, GA, 30308, USA.
Department of Otolaryngology, Emory University, Atlanta, GA, USA.
Endocr Pathol. 2018 Mar;29(1):35-42. doi: 10.1007/s12022-017-9509-0.
Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was recently proposed as a designation for a subset of follicular variant papillary thyroid carcinoma (FVPTC). Encapsulated FVPTC has been shown to be a fairly indolent tumor, and NIFTP are expected to represent the most indolent subset of these tumors. Many of the exclusion criteria for NIFTP related to architecture and a lack of psammoma bodies are designed to preclude the inclusion of more aggressive non-FVPTC tumors in this indolent group and also exclude the diagnosis of FVPTC. In addition to strict application of histologic features to ensure that NIFTP represents a subset of encapsulated FVPTC without invasion, other exclusion criteria including high mitotic activity and necrosis may also lead to a lack of one-to-one correlation between the diagnosis of NIFTP and encapsulated FVPTC without invasion. In this series, 50 cases previously diagnosed as FVPTC over a 2-year period from a large academic center are retrospectively reviewed for reclassification as NIFTP. Additionally, cases not meeting criteria for NIFTP are more accurately classified using the most up to date WHO criteria. Prior BRAF V600E mutation testing was examined for these tumors when available. Seventeen of 50 (34%) tumors met criteria for classification as NIFTP and, 17 (34%) were classified as encapsulated FVPTC with invasion. Strict application of architectural features led to classification of 12 (24%) tumors as non-FVPTC with a variety of more aggressive designations. Tumors classified as NIFTP and encapsulated FVPTC with invasion lacked lymph node metastases (0/4; 0/7, respectively) and BRAF mutations (0/12; 0/13, respectively). In contrast, infiltrative FVPTC, encapsulated PTC with or without invasion, and conventional PTC showed more aggressive features with lymph node metastases and BRAF V600E mutations. One case not meeting criteria for NIFTP maintained the diagnosis of encapsulated FVPTC without invasion but demonstrated significant mitotic activity (three mitoses/ten HPF) and lacked lymph node metastases and BRAF V600E mutation. These findings demonstrate the importance of using strict criteria, especially the lack of true papillary architecture, for the diagnosis of NIFTP and encapsulated FVPTC to ensure that only truly indolent tumors will be included in these diagnoses and to allow tumors with potential for more aggressive behavior to be appropriately treated.
非侵袭性滤泡甲状腺肿瘤伴乳头状核特征（NIFTP）最近被提议作为滤泡状变异型甲状腺癌（FVPTC）的一个亚组的命名。已证实包膜型 FVPTC 是一种相当惰性的肿瘤，而 NIFTP 预计代表这些肿瘤中最惰性的亚组。NIFTP 相关的许多排除标准与结构和缺乏砂粒体有关，旨在排除更具侵袭性的非 FVPTC 肿瘤归入这一惰性组，并排除 FVPTC 的诊断。除了严格应用组织学特征以确保 NIFTP 代表无侵袭性的包膜型 FVPTC 的一个亚组外，其他排除标准，包括高有丝分裂活性和坏死，也可能导致 NIFTP 的诊断与无侵袭性的包膜型 FVPTC 之间缺乏一一对应关系。在本系列中，对来自一个大型学术中心的 2 年内先前诊断为 FVPTC 的 50 例病例进行回顾性复习，以重新分类为 NIFTP。此外，不符合 NIFTP 标准的病例使用最新的世卫组织标准更准确地分类。当有条件时，对这些肿瘤进行了先前的 BRAF V600E 突变检测。50 例肿瘤中有 17 例（34%）符合 NIFTP 分类标准，17 例（34%）被归类为有侵袭性的包膜型 FVPTC。严格应用结构特征导致 12 例（24%）肿瘤被归类为具有各种更具侵袭性名称的非 FVPTC。被归类为 NIFTP 和有侵袭性的包膜型 FVPTC 的肿瘤缺乏淋巴结转移（分别为 0/4；0/7）和 BRAF 突变（分别为 0/12；0/13）。相比之下，浸润性 FVPTC、有或无侵袭性的包膜型 PTC 和常规 PTC 具有更具侵袭性的特征，包括淋巴结转移和 BRAF V600E 突变。一例不符合 NIFTP 标准的病例保留了无侵袭性的包膜型 FVPTC 的诊断，但显示出显著的有丝分裂活性（每 10 个高倍视野中有 3 个有丝分裂），且缺乏淋巴结转移和 BRAF V600E 突变。这些发现表明，使用严格的标准，特别是缺乏真正的乳头状结构，对于 NIFTP 和包膜型 FVPTC 的诊断非常重要，以确保只有真正惰性的肿瘤才会被纳入这些诊断，并允许具有更具侵袭性行为潜能的肿瘤得到适当治疗。
