Purpose To investigate the clinicopathological features, histogenesis, morphological characteristics, immunophenotypes and differential diagnosis of primary extragonadal yolk sac tumor ( eYST) . Methods Clinicopathological data, morphological charac-teristics and immunophenotypes results of 40 cases of eYST were retrospectively studied and the relevant literatures were reviewed. Re-sults All 40 patients, which included 24 male and 16 female, aged from 6 months to 42 years with a 12 years average age and 17 (42.5%) cases were over 12 years old. Mediastinum, sacrococcygeal, retroperitoneal, pineal gland and vagina were involved in 16 (40.0%), 12(30.0%), 5(12.5%), 4(10.0%) and 3(7.5%), respectively. All 40 cases included 32(80.0%) cases pure YSTs, while other 8(20.0%) cases contained other one or two types of germ cell tumor (GCT) components. Conclusions Primary eYST is rare, mediastinum and sacrococcygeal are the most common anatomic sites for eYST, and these mediastinal tumor patients are overwhelmingly confined to adult males, whose average age are significantly older than that in sacrococcygeal, retroperitoneal, pineal gland and vaginal tumor patients (P<0.05), while other sites eYST are restricted to prepubertal children. Adult eYST contain other types of GCT components in some cases, and children's counterparts are always pure YST. Extragonadal eYST manifestate pleomorphic histological features, which combine with immunohistochemical markers is definite value for diagnosis, differential diagnosis.%目的：探讨原发性性腺外卵黄囊瘤( extragonadal yolk sac tumor, eYST)的临床病理特征、组织来源、形态学特点、免疫表型及鉴别诊断。方法回顾性分析40例原发性eYST的临床病理资料、形态学和免疫表型特征,结合文献对其临床病理特点进行分析。结果40例eYST中男性24例、女性16例,年龄6个月~42岁,平均12岁,≥12岁者17例,占42.5%。肿瘤分别位于纵隔16例(40.0%)、骶尾12例(30.0%)、腹膜后5例(12.5%)、松果体4例(10.0%)、阴道3例(7.5%)。40例患者中32例为纯YST(80.0%),8例(20.0%)含有1~2种其他类型的生殖细胞肿瘤(germ cell tumor, GCT)成分。结论原发性eYST少见,纵隔和骶尾是eYST最常见的解剖部位；发生在纵隔的肿瘤患者大部分限于成年男性,患者平均年龄明显大于骶尾、腹膜后、松果体和阴道肿瘤的患者(P<0.05),发生在其他部位的eYST多限于青春期前的儿童；一些成人eYST的病例包含其他类型的GCT成分,儿童eYST总是为纯YST；eYST表现出多形性的组织学特征,结合免疫表型对明确诊断、鉴别诊断有一定价值。
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