Thymoma is the most common tumor in mediastinum. In Vietnam, there has not been any study regarding the pathological classification according to 2015 WHO classification, and the expression of imumunohistochemical markers of thymoma. | Journal of military pharmaco-medicine no1-2019 A REVIEW OF THE EXPRESSION OF CLINICAL, PATHOLOGICAL AND IMMUNOHISTOCHEMICAL FEATURES IN 76 CASES OF THYMOMA Tran Ngoc Dung1; Dinh Tien Truong1; Nguyen Khac Tuyen1 Nguyen Manh Hung1; Tran Viet Tien1 SUMMARY Introduction: Thymoma is the most common tumor in mediastinum. In Vietnam, there has not been any study regarding the pathological classification according to 2015 WHO classification, and the expression of imumunohistochemical markers of thymoma. Objectives: To determine these histological types of thymoma and expression of imumunohistochemical markers in thymoma according to 2015 WHO classification. Subjects and methods: 76 patients pathologically diagnosed with thymoma, underwent thymectomy at Department of Thoracic Surgery, 103 Military Hospital, from January 2010 to October 2018. Samples of thymoma were taken and performed H&E staining and imunohistochemical staining with these markers which were CD3, CD20, CD45, CD117, CKAE1/AE3, EMA, CK19, Ki67, p53. Results: A total of 76 patients, mean age ± and mean tumor size ± cm; patients with stage I disease were the most frequent (). of patients had the invasive tumor. of patients had accompanying myasthenia gravis, mostly at stage IIA (). The two most common types of thymic tumors were determined type B1 () and B2 (). Conclusion: Generally, thymoma is rarely exposed on children. There was no difference between genders. The tumor size was quite large. Patients with stage I were the most frequent. The tumor could invade into the capsule. Type B1 and B2 thymoma were the most common. Myasthenia gravis could be found in patients with thymoma. Thymoma had a high mitotic count and poor expression of the mutation in tumor suppressor genes. * Keywords: Thymoma; Myasthenia gravis; Imumunohistochemical features. INTRODUCTION Thymomas are the most common tumors in the mediastinum, represent more than 45% in adults with .