Clinicopathological features of mediastinal B3 thymoma with CD5 and/or CD117 positivity and lack of TdT-positive lymphocytes

LI Xiaoling; CHEN Bohan; HUANG Zhong

doi:10.3969/j.issn.1007-8096.2025.07.009

Abstract：Objective To investigate the clinicopathological characteristics of mediastinal type B3 thymoma with CD5 and/or CD117 positivity and lack of TdT-positive lymphocytes.Methods Two cases of mediastinal B3 thymoma with CD5 and/or CD117 positivity and lack of TdT-positive lymphocytes diagnosed by the Department of Pathology,Affiliated Hospital of Guangdong Medical University from December 2023 to July 2024 were collected.Their clinical pathological characteristics were analyzed and summarized based on the literature review.Results Both patients were male,aged 54 and 73 years,respectively.They had no obvious clinical respiratory symptoms and had no history of smoking.Both patients had anterior mediastinal occupying lesions with tumor diameters of 53 mm and 72 mm,respectively.Under microscope,all tumor cells showed a B3 thymoma-like morphology.Immunohistochemistry showed positive expression of CD5 and/or CD117,and lacked TdT-positive lymphocytes.Both patients expressed MUC1,with some regions expressing GLUT1.Case 1 underwent radical surgical resection and local radiotherapy after surgery,and survived tumor-free for 19 months since follow-up.Case 2 had pleural and liver metastases when he was diagnosed and refused further chemoradiotherapy.He was lost to follow-up 2 months after tumor progression.Conclusion Mediastinal B3 thymoma with CD5 and/or CD117 positivity and lack of TdT-positive lymphocytes is rare and occurs most frequently in men and anterior mediastinum.Combination of morphology and immunohistochemistry with CD5,CD117,TdT,MUC1,and GLUT1 can help to distinguish thymic carcinoma.The biological behavior and survival trend of this tumor may be between type B3 thymoma and thymic carcinoma.There are few relevant research reports,and more cases still need to be accumulated for further in-depth study and analysis.