Introduction: Primary mediastinal large B-cell lymphoma (PMBCL) is a rare and aggressive non-Hodgkin lymphoma originating from mediastinal thymic B cells. Its peculiar molecular signature assists in differentiating it from other subtypes of non-Hodgkin lymphoma.

Case report: We present a rare case of PMBCL in a 39-year-old male with a bulky mediastinal mass that resulted in superior vena cava thrombosis and cardiac tamponade. Diagnostic discordance between histopathological and molecular data led to a delay in interception of this entity. Histopathology findings were suggestive of spindle-cell neoplasm. Contrastingly, next-generation sequencing (NGS) and immunohistochemistry (IHC) yielded a molecular diagnosis of PMBCL. IHC staining revealed that the atypical cells were positive for CD20, PAX5, CD79a, CD30, CD23, MUM1, and weakly positive for MAL (myelin and lymphocyte) protein. NGS showed increased expression of TNFRSF8 and CD274 genes, which encode CD30 and PDL1 proteins, respectively. The patient was successfully treated with the R-Hyper-CVAD protocol without consolidative radiotherapy.

Conclusion: Diagnosing PMBCL can be challenging because it lacks pathognomonic features and shares characteristics with other lymphomas. Molecular testing is of paramount importance in this context owing to its distinctive immunophenotype.

Keywords: B-cell lymphoma; Diffuse large B-cell lymphoma; Non-Hodgkin lymphoma; Primary mediastinal large B-cell lymphoma; R-Hyper-CVAD.

© 2025 The Author(s). Published by S. Karger AG, Basel.

简介： 原发纵隔大B细胞淋巴瘤（PMBCL）是一种罕见且具有侵袭性的非霍奇金淋巴瘤，起源于纵隔胸腺B细胞。其独特的分子特征有助于将其与其他类型的非霍奇金淋巴瘤区分开来。

病例报告： 我们报道了一例39岁男性患者的罕见PMBCL案例，该患者患有巨大的纵隔肿块，并导致上腔静脉血栓和心包填塞。病理组织学检查与分子数据之间的诊断不一致延迟了对该疾病的识别。病理检查结果提示为梭形细胞肿瘤。相反，下一代测序（NGS）和免疫组化（IHC）结果显示该患者患有PMBCL。IHC染色显示异型细胞表达CD20、PAX5、CD79a、CD30、CD23、MUM1，以及轻微的MAL蛋白（髓鞘和淋巴细胞相关）。NGS结果显示TNFRSF8和CD274基因表达增加，分别编码CD30和PDL1蛋白。患者成功接受了R-Hyper-CVAD方案治疗，未进行巩固性放疗。

结论： 诊断PMBCL具有挑战性，因为它缺乏特异性病理特征，并且与其他淋巴瘤有共同之处。鉴于其独特的免疫表型，在这种情况下分子检测尤为重要。

关键词： B细胞淋巴瘤；弥漫大B细胞淋巴瘤；非霍奇金淋巴瘤；原发纵隔大B细胞淋巴瘤；R-Hyper-CVAD。