Intrathyroid thymic carcinoma (ITTC) is a rare malignant neoplasm considered to be a eutopic thymic carcinoma (TC) arising ectopically in the thyroid. Histopathologically, ITTC resembles squamous cell carcinoma of the thymus with positive TC markers such as CD5 and c-KIT. Despite these similar histological findings, ITTC is clinically less aggressive than TC. In this study, we compared clinical, histological, and genetic characteristics of ITTCs and TCs. We collected 9 ITTCs and 8 TCs with their clinicopathological profiles. Immunohistochemistry for CD5, p63, CD117/c-KIT, Ki-67, p53, TTF-1, thyroglobulin, PAX8, EGFR, and PD-L1/CD274 plus in situ hybridization for EBER was performed. We further investigated mutation status of KIT, EGFR, BRAF, and TERT promoter using Sanger sequencing. In our study, ITTCs affected significantly younger patients than TCs. After a mean follow-up of 86 months, all patients with ITTC were alive, while two patients with TC had died. Immunohistochemistry showed ITTCs and TCs had a similar immunophenotype except for EGFR and p53. Genetic analysis did not identify KIT or BRAF mutations in any ITTCs or TCs. EGFR mutations were positive in 11% (1/9) of ITTCs and 25% (2/8) of TCs. Notably, TERT promoter C228T mutation was identified in 22% (2/9) of ITTCs but none of the TCs. There were no significant differences in age, tumor size, or sex between TERT-mutated and TERT-wild-type ITTCs. Collectively, ITTC and TC have similar histopathologic and immunophenotypic features but different clinical outcomes. Recurrent TERT promoter mutation may be a key event related to cancer progression in ITTCs and warrants further investigation.

中文翻译：

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甲状腺内胸腺癌中复发性TERT启动子突变的鉴定。

甲状腺内胸腺癌（ITTC）是一种罕见的恶性肿瘤，被认为是异位在甲状腺中产生的异位胸腺癌（TC）。在组织病理学上，ITTC类似于带有阳性TC标记物（如CD5和c-KIT）的胸腺鳞状细胞癌。尽管有这些相似的组织学发现，但ITTC在临床上没有TC更具侵略性。在这项研究中，我们比较了ITTC和TC的临床，组织学和遗传学特征。我们收集了9个ITTC和8个TC及其临床病理特征。进行了CD5，p63，CD117 / c-KIT，Ki-67，p53，TTF-1，甲状腺球蛋白，PAX8，EGFR和PD-L1 / CD274的免疫组织化学以及EBER的原位杂交。我们进一步调查了KIT，EGFR，BRAF和使用Sanger测序的TERT启动子。在我们的研究中，ITTC比TC明显影响年轻患者。在平均随访86个月后，所有ITTC患者均存活，而两名TC患者已死亡。免疫组织化学显示，除了EGFR和p53外，ITTC和TC具有相似的免疫表型。遗传分析未发现任何ITTC或TC中的KIT或BRAF突变。在11％（1/9）的ITTC和25％（2/8）的TC中，EGFR突变呈阳性。值得注意的是，在22％（2/9）的ITTC中发现了TERT启动子C228T突变，但没有一个TC。TERT突变和TERT之间的年龄，肿瘤大小或性别无明显差异-野生型ITTC。总的来说，ITTC和TC具有相似的组织病理学和免疫表型特征，但临床结果不同。复发的TERT启动子突变可能是与ITTC中癌症进展相关的关键事件，值得进一步研究。