Anaplastic thyroid carcinoma (ATC) demonstrates a wide variety of morphologies and is characteristically associated with a differentiated thyroid carcinoma component. Heterologous differentiation is a rare, potentially challenging phenomenon in ATC, mostly observed as osteosarcomatous or chondrosarcomatous differentiation. We now describe a novel ‘glomangiosarcoma-like’ differentiation, review our archival experience from two institutions (UPMC, CC), and perform a systematic review for the prevalence of heterologous elements in ATC. The patient is a 57-year-old female who presented with 4.5 cm left thyroid, and 3.4 cm neck masses. Histologically, the thyroid demonstrated a differentiated high grade papillary thyroid carcinoma, tall cell and hobnail/micropapillary subtypes transitioning into an anaplastic component with spindled to ovoid cells with hemangiopericytoma-like vasculature showing CD34 positivity, variable muscle marker expression and pericellular lace-like type IV collagen deposition. The neck mass consisted solely of the latter morphology. Targeted next-generation sequencing was performed on high grade DTC and adjacent ATC from the thyroid as well as ATC from the neck metastasis. All three components shared BRAF^V600E, TERT promoter, and PIK3CA mutations confirming a clonal origin. Archival (UPMC: n = 150, CC: n = 74) and literature review showed no prior examples. Systematic review and meta-analysis of prevalence showed a baseline pooled prevalence (generalized linear mixed model) of heterologous elements of any type to be 1.6% (95% confidence interval: 1.0–2.6%) for studies where this was specifically addressed. ATC with glomangiosarcoma-like heterologous differentiation is a rarity among an already rare morphologic category with unique diagnostic pitfalls.

甲状腺未分化癌（ATC）表现出多种形态，并且与分化型甲状腺癌成分相关。异源分化是 ATC 中一种罕见的、具有潜在挑战性的现象，主要观察为骨肉瘤或软骨肉瘤分化。我们现在描述了一种新的“血管肉瘤样”分化，回顾了两个机构（UPMC、CC）的档案经验，并对 ATC 中异源元素的流行情况进行了系统回顾。患者是一名 57 岁女性，左侧甲状腺 4.5 厘米，颈部肿块 3.4 厘米。组织学上，甲状腺表现出分化的高级别甲状腺乳头状癌，高细胞和平头钉/微乳头状亚型转变为间变性成分，具有梭形至卵圆形细胞，具有血管外皮细胞瘤样脉管系统，显示 CD34 阳性、可变肌肉标志物表达和细胞周花边状 IV 型胶原沉积。颈部肿块仅由后一种形态组成。对来自甲状腺的高级别 DTC 和邻近的 ATC 以及来自颈部转移的 ATC 进行了靶向下一代测序。所有三个组件均具有BRAF ^V600E、TERT启动子和PIK3CA突变，证实了克隆起源。档案（UPMC：n = 150，CC：n = 74）和文献综述显示没有先前的例子。对流行率的系统审查和荟萃分析表明，对于专门解决这一问题的研究，任何类型的异源元素的基线汇总流行率（广义线性混合模型）均为 1.6%（95% 置信区间：1.0–2.6%）。具有血管肉瘤样异源分化的 ATC 在已经罕见的形态学类别中非常罕见，具有独特的诊断缺陷。