Suster S, Moran C A, Chan J K
Arkadi M. Rywlin Department of Pathology and Laboratory Medicine, Mount Sinai Medical Center and University of Miami School of Medicine, Florida 33140, USA.
Am J Surg Pathol. 1997 Nov;21(11):1316-23. doi: 10.1097/00000478-199711000-00006.
Six cases are described of an unusual type of primary thymic epithelial neoplasm characterized by a biphasic epithelial/spindle cell morphology that closely resembled a carcinosarcoma. The patients were two women and four men 28-70 years of age. The tumors presented clinically as asymptomatic anterior mediastinal masses found incidentally on routine chest radiographs. All patients were treated by complete surgical excision. Grossly, the tumors consisted of well-circumscribed, encapsulated masses that measured 6-14 cm in greatest diameter and showed a gray-white, homogeneous, rubbery cut surface. Histologically, the lesions were composed of anastomosing islands and cords of oval to polygonal epithelial cells displaying large nuclei with occasional prominent nucleoli and rare mitotic figures, separated by areas containing a highly cellular spindle cell proliferation without nuclear atypia. Thymic remnants could be identified in the periphery of the lesions in four cases. Immunohistochemical stains showed diffuse strong positivity for keratin and focally for epithelial membrane antigen (EMA) in the epithelial cell component, and strong positivity for vimentin and focally for actin in the spindle cell stromal component. Stains for keratin, EMA, desmin, S-100 protein, and CD34 were negative in the spindle stromal cells in all cases except one, in which EMA positivity was present; CD5 stains were negative in the epithelial cells in all cases examined. Electron microscopic examination in one case showed well-formed desmosomes and tonofilaments in the epithelial elements, as well as features indicative of fibroblastic differentiation in the spindle stromal cells. Because of the unusually florid spindle cell stromal component and the focally atypical features of the epithelial cells, some of these tumors initially were misinterpreted as examples of carcinosarcoma. Clinical follow-up in five cases showed that the patients were alive and without evidence of disease over a period of 5-20 years (mean follow-up 10 years), suggesting a benign or very low grade malignant biologic behavior. The present cases appear to represent an unusual, previously undescribed morphologic variant of thymoma characterized by a prominent pseudosarcomatous stromal component. Because of the distinctive histologic appearance and indolent clinical behavior, these lesions should be distinguished from other more aggressive anterior mediastinal neoplasms displaying a biphasic morphology.
本文描述了6例不寻常类型的原发性胸腺上皮肿瘤，其特征为具有双相上皮/梭形细胞形态，与癌肉瘤极为相似。患者包括2名女性和4名男性，年龄在28至70岁之间。这些肿瘤临床上表现为在常规胸部X线检查时偶然发现的无症状前纵隔肿块。所有患者均接受了完整的手术切除。大体上，肿瘤为边界清楚、有包膜的肿块，最大直径为6至14厘米，切面呈灰白色、均匀、似橡胶样。组织学上，病变由相互吻合的椭圆形至多边形上皮细胞岛和索组成，细胞核大，偶见明显核仁，罕见有丝分裂象，其间为细胞丰富的梭形细胞增殖区，无核异型性。4例病变周边可识别出胸腺残余。免疫组化染色显示，上皮细胞成分中角蛋白弥漫强阳性，上皮膜抗原（EMA）局灶阳性；梭形细胞间质成分中波形蛋白强阳性，肌动蛋白局灶阳性。除1例EMA阳性外，所有病例梭形间质细胞中角蛋白、EMA、结蛋白、S-100蛋白和CD34染色均为阴性；所有检查病例的上皮细胞中CD5染色均为阴性。1例的电镜检查显示上皮成分中有发育良好的桥粒和张力丝，梭形间质细胞有提示成纤维细胞分化的特征。由于梭形细胞间质成分异常丰富，上皮细胞有局灶非典型特征，部分肿瘤最初被误诊为癌肉瘤。5例患者的临床随访显示，在5至20年期间（平均随访10年）患者存活且无疾病证据，提示其生物学行为为良性或极低级别恶性。目前这些病例似乎代表了一种不寻常的、以前未描述过的胸腺瘤形态学变异型，其特征为显著的假肉瘤样间质成分。由于其独特的组织学表现和惰性的临床行为，这些病变应与其他表现为双相形态的更具侵袭性的前纵隔肿瘤相鉴别。
