Institute of Pathology, Ingolstadt, Germany.
Virchows Arch. 2014 Sep;465(3):313-20. doi: 10.1007/s00428-014-1606-6. Epub 2014 Jun 13.
Due to its profound therapeutic consequences, the distinction between thymoma and T-lymphoblastic lymphoma in needle biopsies is one of the most challenging in mediastinal pathology. One essential diagnostic criterion favouring thymoma is the demonstration of increased numbers of keratin-positive epithelial cells by immunohistochemistry. Loss of keratin expression in neoplastic epithelial cells could lead to detrimental misdiagnoses. We here describe a series of 14 thymic epithelial tumours (11 type B2 and B3 thymomas, 3 thymic carcinomas) with loss of expression of one or more keratins. Cases were analysed for expression of various keratins and desmosomal proteins by immunohistochemistry and immunofluorescence and compared with 45 unselected type B thymomas and 24 thymic carcinomas arranged in a multitissue histological array. All 14 cases showed highly reduced expression of at least one keratin, three cases were completely negative for all keratins studied. Of the 14 cases, 13 showed strong nuclear expression of p63. Expression of desmosomal proteins was preserved, suggesting intact cell contact structures. Loss of expression of broad-spectrum-keratins and K19 was observed in 3 and 5 % of unselected thymomas and in 30 and 60 % of thymic carcinomas. A proportion of keratin-depleted thymomas contained giant cells, reminiscent of thymic nurse cells. Loss of keratin expression in type B2 and B3 thymomas is an important diagnostic pitfall in the differential diagnosis with T-lymphoblastic lymphoma and can be expected in 5 % of cases. A panel of epithelial markers including p63 is warranted to ensure correct diagnosis of keratin-negative mediastinal tumours.
由于其深远的治疗后果，在针吸活检中区分胸腺瘤和 T 淋巴母细胞性淋巴瘤是纵隔病理学中最具挑战性的问题之一。支持胸腺瘤的一个重要诊断标准是免疫组织化学显示上皮细胞角蛋白阳性细胞数量增加。肿瘤上皮细胞角蛋白表达缺失可导致诊断错误。我们在此描述了 14 例胸腺癌（11 例 B2 和 B3 胸腺瘤，3 例胸腺癌），其表达一种或多种角蛋白缺失。通过免疫组化和免疫荧光分析对各种角蛋白和桥粒蛋白的表达进行了分析，并与 45 例未选择的 B 型胸腺瘤和 24 例胸腺癌进行了比较，这些病例排列在多组织组织学阵列中。所有 14 例均显示至少一种角蛋白的高度表达减少，3 例对所有研究的角蛋白均完全阴性。在 14 例病例中，有 13 例 p63 核表达强烈。桥粒蛋白的表达保持不变，表明细胞接触结构完整。广谱角蛋白和 K19 的表达缺失在未选择的胸腺瘤中分别观察到 3%和 5%，在胸腺癌中分别观察到 30%和 60%。一部分角蛋白耗竭的胸腺瘤含有巨细胞，类似于胸腺滋养细胞。B2 和 B3 胸腺瘤中角蛋白表达缺失是与 T 淋巴母细胞性淋巴瘤鉴别诊断的重要陷阱，预计在 5%的病例中会出现。包括 p63 在内的一组上皮标志物是确保正确诊断角蛋白阴性纵隔肿瘤所必需的。
